ELEMENTS OF THE PRACTICE OF PHYSIC.
PART THE FIRST.
CONTAINING THE NATURAL HISTORY OF THE HUMAN BODY.
BY GEORGE FORDYCE, M.D.
Of the Royal College of PHYSICIANS, and Reader on the PRACTICE of PHYSIC in LONDON.
LONDON: Printed for JOHNSON and PAYNE (at No. 8.) In Pater-noster Row.
M DCC LXX.
[Price One Shilling and Six-pence.]
THIS ESSAY ON THE ART OF HEALING, IN TESTIMONY OF THE AUTHOR'S GRATITUDE, IS WITH THE GREATEST RESPECT, INSCRIBED TO HIS GRACE HUGH DUKE OF NORTHUMBERLAND, A LOVER AND A PROMOTER OF USEFUL ARTS, BY HIS GRACE'S MOST OBEDIENT SERVANT, GEORGE FORDYCE.
THE NATURAL HISTORY OF THE HUMAN BODY.
A Disease is such an alteration of the chemical properties of the fluids or solids, or of their organization; or of the action of the moving power; as produces an inability or difficulty of performing the functions of the whole, or any part of the system, or pain, or a preternatural evacuation.
The CHEMICAL PROPERTIES of the FLUIDS.
THE fluids may be divided into
- 1st, The blood.
- 2dly, Those formed during digestion, before the food is converted into blood.
- 3dly, The secreted fluids.
The blood consists of
- 1st, The serum.
- 2dly, The coagulable lymph,
- 3dly, The red part.
- 4thly, The superfluous water.
- 5thly, Extraneous substances introduced.
The serum, coagulable lymph, and superfluous water, are diffused through one another; and the red part is mechanically mixed with them. Some of the extraneous substances are also mechanically mixed with them, and some diffused through them.
PROPERTIES of the SERUM.
IT is fluid in any degree of heat between 30 and 160 of Fahrenheit's thermometer.
In a lesser heat it freezes, in a greater it coagulates.
Coagulation is a separation of an animal or vegetable matter from the water in which it was dissolved; and is at the same time a change of the properties of that matter, rendering it insoluble in water again by commixture alone.
The serum consists chemically of a coagulable matter, and water in which common sal ammoniac and phosphoric ammoniac, and generally common salt, and frequently selenites, and fixed ammoniac, are dissolved; but it is a question, whether the water chemically combined in the serum is also united with those neutral salts, or whether the serum, and the solution of these, are only diffused through one another.
It is probably in itself colourless, and inodorous; but it receives a yellowish or brownish hue from the putrescent part of the blood, and acquires a smell from the essential oil.
If it contained no neutral salts, it would be insipid, and incapable of stimulating.
The superfluous water may be separated from it by filtration in the body, but that which is chemically combined with the other parts cannot.
All the water may be evaporated from it by a lesser heat than 140 degrees of Fahrenheit's thermometer, if it be exposed to the air. The other parts remain after this operation solid, and soluble again in water by commixture alone.
The separation or addition of superfluous water does not affect its viscidity, so far as that is of any consequence in the circulation; but the separation of that water which is in chemical combination, may render it more viscid.
The water in chemical combination is never separated, while the serum is contained in the blood-vessels; and of consequence this part of the blood is always equally viscid, so far as its viscidity can affect the circulation or secretions.
It may be coagulated by acids, oils, alcohol, &c. but no substance can get into the blood-vessels in a sufficient degree of concentration to coagulate it, excepting by injection.
It may be coagulated by a juice secreted in the stomach.
It has seldom, if ever, been found coagulated in the body.
The only perceptible difference which has appeared in the coagulable part of the serum, from any observation hitherto made public, is, that sometimes in coagulating its parts▪ adhere more or less firmly, and that sometimes it is of a deeper or lighter brown colour.
PROPERTIES of the COAGULABLE LYMPH.
IT is a compound of water and a coagulable matter.
As long as it continues in the course of circulation, it is fluid in any degree of heat between 30 and 120 degrees of Fahrenheit's thermometer.
When it is taken out of the blood-vessels, it coagulates; whether it be in motion or at rest, exposed to the air or not, or in the heat of the human body, or in any other degree of heat.
If it be retained in a blood-vessel, it continues fluid for more than three hours in any degree of heat between 30 and 120 of Fahrenheit's thermometer, and that whether it be in motion or at rest. The smaller the blood-vessel, the longer it continues fluid.
It has hardly ever been found coagulated in the blood-vessels of a living animal, unless they have been enlarged into aneurisms or varices.
It has generally been found coagulated in the large vessels of the human body on dissection, and sometimes separated from the other parts; but to all appearance these coagulations have almost always taken place after death.
When it is taken out of the blood-vessels, it may be prevented from coagulating, by saturating the whole blood with common, sea-salt, and perhaps by some of the other neutral salts.
Although the coagulable part of the serum and coagulable lymph have different properties, the coagulum formed from both is pretty nearly the same.
The coagulum may be dissolved in water by boiling or putrefaction; and may be united with concentrated acids, with caustic alkalis, and calcarious earth, and with some metallic salts, into a substance soluble in water: but none of these can get into the system by absorption, so as to produce this effect.
Both the superfluous water and serum are capable of being separated from the coagulable lymph, by filtration in the body.
When the blood is received into a proper vessel, the coagulation of this part gives an appearance of solidity to the whole: but soon after the whole becomes thus apparently solid, part of the serum, of the superfluous water, and of the water which was combined with the coagulable lymph, ouzes out from the whole mass, and brings along with it part of any extraneous fluid that may be contained in the blood-vessels; leaving behind what is commonly called the red globules, the coagulum of the coagulable lymph, and any solid particles that may have been in the blood. This is called the spontaneous separation.
When the arteries are acting strongly, whether the whole habit be strong or not, the coagulable lymph is more fluid, and longer in coagulating. Of consequence it lets the red particles, which are the heaviest part of the blood, fall down towards the bottom, before it coagulates: and upon the spontaneous separation, the coagulum is divided into two parts; the upper, consisting of the coagulum of the coagulable lymph alone (which has in this case been called the buff); the under, consisting partly of this, and partly of the red particles.
Although part of the coagulable lymph would separate from the red particles, may be prevented by taking the blood from a small vessel, or from a small [Page 6]orifice, or by letting it run along the skin before it falls into the vessel into which it is received, or by receiving it into a vessel whose surface is large in proportion to its contents; as in all these cases the coagulation is forwarded. On the other hand, if it stagnate in the blood-vessel for some time before it is taken out, there will be a separation, when none would otherwise have happened.
Whether the coagulable lymph separates in part from the red particles, or not, it coagulates sometimes into a firmer, sometimes into a looser mass, generally in proportion to the strength of the system.
All the substances which coagulate the serum, have the same effect on the coagulable lymph; but none can be applied to it in the blood-vessels, excepting by injection in a sufficient degree of concentration to coagulate it.
The coagulable lymph is probably in itself colourless, insipid, inodorous, and incapable of stimulating.
Whilst it remains in the blood-vessels, it is chemically combined with a certain proportion of water, from which it cannot be separated but by coagulation; neither will it combine with a larger proportion.
Water mechanically mixed with it has no effect on its viscidity, so far as that affects the circulation or secretions.
No other differences besides those already taken notice of are observable in its properties.
The coagulable lymph and serum are both capable of putrefaction, and are converted by it into a mucilaginous matter, not coagulable by any of the methods recited above.
If this mucilaginous matter should undergo a further putrefaction, it emits a foetid vapour, and is converted into saline substances and calcarious earth.
PROPERTIES of the RED PART.
UPON viewing this part of the blood with a deep magnifier in the solar microscope, as it circulates in the blood-vessels of a living animal, it appears to be divided into a number of small particles, which are apparently annular, and exceedingly flexible.
While the animal is respiring, and the blood circulating, it is of a scarlet colour in the arteries, and of a Modena red in the veins; but if the respiration be stopped, that blood which circulates afterwards through the lungs continues of a Modena red. If it be taken out of the veins, kept moist, and exposed to respirable air, it becomes of a scarlet colour; if it be taken out of the arteries, and covered from the air, or if it stagnate in them, its colour is changed to a Modena red. A light shade of Modena red is not scarlet, neither is a deep scarlet a Modena red. Various other substances alter the colour of this part.
It seems to have a sweetish tasle, to be inodorous, and void of stimulus.
Its specific gravity is but a very little more than the serum or coagulable lymph.
It is more inflammable than the other parts; and, on performing its chemical analysis, it yields a large proportion of empyreumatic oil.
It is readily soluble in water, but not in the serum.
It is not soluble in a saturated solution of neutral salts.
It is capable of undergoing the putrefactive fermentation, the first stage of which breaks it down into smaller particles, and renders it of a dark colour. It afterwards is converted into a mucilage, and becomes soluble in the serum.
The SUPERFLUOUS WATER.
IT is diffused through the serum and coagulable lymph.
It contains a part, perhaps the whole, of the salts.
These salts are chemically combined with a part of it only, and this solution is diffused through the remaining part.
The water diffused may be separated from the solution by filtration in the body.
The solid part of the blood, left after evaporation of the water by a beat lest than that of boiling water, amounts to from one fourth to one fifth of the whole.
EXTRANEOUS SUBSTANCES.
A Great variety of extraneous substances, both fluid and solid, may be introduced into the blood-vessels by absorption; but none of them in such proportion as to produce any alteration in the blood, except by fermentation.
When any ferment is introduced into the blood-vessels, it acts upon a part of the blood only; the greatest part remaining to all experiment exactly the same as before.
Of the PUTREFACTION of the BLOOD.
FErmentation is the conversion of one compound into another, by a new arrangement or manner of combination of its elements.
What is commonly called putrefaction consists of two fermentations, which we shall call by the names of the first and second stage.
All animal solid and fluids may be reduced by the first into a mucilaginous mass, soluble in water, and diffusible through any quantity of it.
The red part of the blood first breaks down into smaller particles, before it is formed into a perfect mucilage.
The first stage takes place without any effervescence.
The second stage converts this mucilage into earths, and salts, a foetid vapour, and fixable air.
The first and second stage of putrefaction take place in a small part of the blood, or it is destroyed by some other operation; for
After having coagulated the serum, if we squeeze out the water, and evaporate it, there is left a mucilaginous matter similar to that formed by putrefaction.
The sails formed in the blood-vessels, excepting phosphoric ammoniac, may be formed by the last stage of putrefaction; and those formed by the last stage are found in the blood-vessels, excepting nitrous selenites, and nitrous ammoniac.
This mucilage, and these salts, are always carrying off by urine; the present blood is always diminishing, and die vessels require a fresh supply from the food.
The blood is always in the most powerful circumstances of putrefaction; which are, a heat of 98 degrees of Fahrenheit's thermometer, fluidity, a moderate exposure to air, and motion: but it is prevented from petrifying by the action of the vessels; nor can any ferment or other circumstance induce the fermentation, till this action is altered, except perhaps the introduction of chyle intermixed with putrid matter.
In diseases, the first stage often takes place in part of the blood; the second stage sometimes, although seldom.
Of DIGESTION.
DIGESTION is the conversion of the food into chyle, and afterwards into blood.
The food may consist of farinaceous or mucilaginous vegetable substances, or native vegetable acid, or sugar, or expressed oil, or animal solids, or animal fluids containing a mucilaginous matter.
These substances may be digested, if they be taken singly, or if they be mixed together.
The blood formed does not differ sensibly in its properties, whether the one or the other of them be used singly, or several of them together; provided the organs of digestion be sufficiently powerful convert them into blood.
If the food be solid, it is generally broke down by the teeth, or by some other apparatus.
But mashing it down with water is not sufficient to alter its chemical properties, and convert it into chyle and blood.
It is mixed in the stomach with the watery fluids we drink, and with the mucilaginous watery fluids secreted by the salivary and other glands.
It is sometimes dissolved in water before it is used: but it is often rendered solid by a previous preparation, or coagulated by a substance secreted in the stomach.
Simple solution in water does not convert it into chyle or blood.
If it be previously dissolved in water, it affords less nourishment than if exhibited solid.
It is necessary that it remain in the stomach for some time, in order to its digestion.
The only process it can go through in the organs of digestion, that is capable of altering its chemical properties, is fermentation.
Its fermentation is not attended with effervescence in a healthy stomach.
If vegetable food be used, an acid is produced. This acid is destroyed in the duodenum by the bile.
If animal food be used alone, no acid is produced.
The stronger the stomach, and the more perfect the digestion, the lese acid is formed from vegetable food.
No stage of the putrefactive fermentation takes place, during the conversion of it into chyle and blood, if the digestion be perfect.
The fermentation which takes place is peculiar to the organs of digestion, and has never been produced by any artificial means yet attempted.
The fermentation which takes place in the stomach, forwards the solution of solid food in the watery menstruums.
Solid foods dissolve sooner in the stomach than they can be dissolved in water in the same heat, by any means hitherto found out.
If the stomach does not act properly, solid food remains undissolved; vegetable, and mixtures of vegetable, and animal substances become more acid; animal substances putrify; a quantity of air is separated; and the food is not digested and converted into chyle.
Only that part of the food which is digested affords nourishment; the nourishment therefore is in proportion to the food and the digestion.
When food, either from its quantity or quality, cannot be digested, it is apt to occasion great disturbances [Page 13]in the system, while it is contained in the stomach and intestines.
The only sensible alterations produced in the blood by different foods, are in its quantity; or in the proportion of superfluous water; or that sometimes a long use of animal food brings on a degree of putrefaction.
Of the CHYLE.
THE chyle is formed from the food in the intestines, and absorbed by the lacteals.
The whole fluid absorbed is not chyle, but a mixture of chyle, and the solution of those substances, which were simply dissolved in water without being digested.
Quere, Whether a simple solution of mucilaginous, animal, or vegetable substances, can be converted into blood, without being formed into chyle in the stomach and intestines?
Chyle is fluid, while in the lacteals; when exposed to the air, it coagulates; it is rendered white, from a mixture of expressed oil.
When coagulated, a fluid may be squeezed out, which probably contains a coagulable matter, and sugar.
THE SECRETED FLUIDS.
THEY either
Exist in the blood-vessels, being mechanically mixed with the other fluids, and require only a mechanical separation;
Or they do not exist in the blood-vessels, their elements only being contained there: but these elements are not combined, so as actually to form the secreted fluid. It is therefore requisite, that some chemical operation should take place in the secretory organ, by which the elements shall be combined so as to form the matter secreted.
The chemical operation by which they are formed, is fermentation.
The fluids separated mechanically, are
- The matter of the insensible perspiration.
- The urine.
- The sweat.
- The milk.
The fluids formed in the secretory organ by a chemical operation, are
- The mucus.
- The saliva.
- The pancreatic juice.
- The semen.
- The bile.
- The wax in the ear.
- The sebaceous matter.
- The coagulating matter of the stomach, &c.
The MATTER of the INSENSIBLE PERSPIRATION.
IT is separated from the surface of the lungs, and from the skin, by evaporation.
The quantity evaporated depends upon the quantity of superfluous water in the blood-vessels, the heat of the air, the quantity of air applied, and the contraction or relaxation of the vessels from whence the evaporation takes place.
When the body is in its natural state, that part of the insensible perspiration, which is capable of condensation, consists of water, with a very small proportion of a mucilaginous matter and essential oil, and sometimes perhaps volatile alkali.
There is no reason to suppose, that any matter flies off that cannot be condensed, from any, experiment hitherto made; but it is rather probable that there is not.
Should any other substance, capable of emitting vapour in the heat of the human body, get into the blood-vessels, or be formed on the surface of the skin, lungs, or in any of the passages of the air in breathing, it may be mixed with the insensible perspiration.
Some of these substances may be putrid vapour, variolous, morbillous, and other infectious matters, alcohol, and other extraneous volatile substances, &c.
The matters thrown off by insensible perspiration, may be evacuated by the other excretions.
The health is not in proportion to the quantity of insensible perspiration.
The URINE.
THE urine, in the common state of the body, is a transparent brownish fluid, which upon cooling has a mucilaginous matter separated, capable of being redissolved in heat.
In health, the separating mucilage is generally in such quantity as to remain suspended in the urine after its reparation, forming what has been called the cloud.
It is sometimes totally absent in health, but much more frequently in diseases; sometimes it is in quantity sufficiently to carry the cloud to the bottom, and form a mucous sediment; and sometimes it falls down in a flaky powder, and forms what bas been called a lateritious sediment, which is commonly of a brick colour, and now and then white.
This last appearance often takes place on the going off of acute diseases; but it also happens in health, and while diseases subsist in their full force, particularly when they affect the urinary, passages, or parts near them.
Sometimes the separating mucilage is separated in a powder, remains suspended in the urine, and renders it turbid.
After the separating mucilage is separated, if the urine be filtrated from it, it is transparent, consisting of water which contains a mucilage, and salts.
1st, A mucilage, similar to that formed by the first stage of putrefaction.
This mucilage is of a brownish colour, and gives the greatest part of the colour to the urine.
Its quantity varies considerably; but the proportion of it in the urine is always small.
If the water be evaporated from it, it will redissolve, and it may be diffused through any quantity of water in any heat.
It is not coagulable.
2dly, The salts are common salt, common sal ammoniac, phosphoric ammoniac, vitriolic selenites, and muriatic selenites.
Common salt is contained in the urine, in consequence of its being used in the food, or drink; and it is in proportion to the quantity used.
The other salts are contained in the urine independent of any saline substance taken into the body, except perhaps the vitriolic selenites.
The quantity of selenitic salts is commonly very small; but sometimes the urine is saturated with vitriolic selenites, which separates, and chrystalizes, upon the urine's standing to cool.
The proportion of the salts varies considerably, but is always so small as to form a diluted solution.
The solution is generally sufficiently concentrated, to stimulate a very irritable part, but not always.
The dilution depends on the quantity of superfluous water in the blood-vessels, and on the quantity of that superfluous water evacuated by the kidneys: so that, when the quantity secreted is large, the solution is generally diluted; when small, more concentrated.
Watery fluids may pass through the blood-vessels, and by the kidneys, hardly carrying off any thing with them, especially if large quantities be drank at a time, and the external vessels be contracted.
Sometimes a quantity of calcareous earth is found in the urine, suspended by mechanical mixture, or at least not combined with an acid.
Any extraneous substance, soluble in water, that may get into the blood-vessels, may be evacuated along with the urine; such as acids, alkalies, neutral and other saline substances; infusion of rhubarb, and other mucilaginous vegetable juices; bile, pus, and other fluids formed in the body.
If the kidneys are relaxed, or stimulated; chyle, serum, coagulable lymph, and even the red part of the blood may be thrown out.
The red part may also be broke down by putrefaction, and pass off by the kidneys, of a very dark colour, disturbing the transparency, and sometimes forming a sediment.
If the heart and arteries act more strongly, or frequently, than they do in their natural state, a quantity of expressed oil comes away with the urine, and forms a film on the surface, or a ring round the vessel into which it is received.
The urine always contains a portion of the essential oil of the urinary passages, and sometimes a portion of their mucus.
The SWEAT.
AS far as we are capable of judging from the small quantity that can be collected, it contains nearly the same substances as the urine; only that instead of the essential oil of the urinary passages, it is mixed with the sebacious matter of the skin, which gives it a degree of whiteness, and a smell different from that of the urine.
The MILK.
IT is secreted naturally in the breasts of women for the nourishment of their young, sometimes during pregnancy, and always after child-birth. There are said to have been instances of its being secreted at other times, and from other parts of the body.
It is a whitish fluid, which separates into two parts upon being left at rest in a moderate degree of heat: The upper part consists principally of expressed oil, with a mixture of the other part, and is whiter and more opaque.
The under part consists of a solution of coagulable matter and sugar, in water; with a small mixture of expressed oil, and is called the skim-milk.
The expressed oil is fluid in the heat of the human body, but solid in the heat of the atmosphere.
It is only mechanically mixed with the other part.
It is tinged with, and receives a flavour from, the essential oil of the food and of the body.
It is found not only in different proportions in the milk of different women, but also in the milk of the same woman at different times, and even in that which issues from the different excretory ducts of the glands of the same breast.
The coagulable matter only differs from the coagulable matter of the serum, in its coagulability, and its proportion to the water.
It is not coagulable by a less heat than that of boiling water, and by that only, if the water be evaporated from it.
It may be coagulated by acids, alcohol, several metallic and aluminous salts, and vegetable juices; but it requires that they should be applied to it in a greater degree of concentration than the serum does, in order to its coagulation.
Heat assists the coagulating power of these substances.
It is readily coagulable by the coagulating juices of the stomach, and coagulates in the stomach of a living animal, whether any acid be contained in it or not.
The sugar contained in the milk does not differ in its properties from that of the sugar-cane.
Its proportion is always small.
When a woman makes use of vegetable food, it seems to be in greater proportion than when she uses animal.
The milk of a bitch, using animal food alone, contains sugar.
If milk be kept for some time exposed to the air, and in the heat of the atmosphere, or of the human body, the sugar ferments, and is converted into vinegar, which coagulates the coagulable matter.
The same change may take place in the breast, if it stagnate there for some time, or if the woman be suddenly affected with any of the passions of the mind that are attended with anxiety.
If blood be taken from the arm after a full meal, the serum is often mixed with a substance which gives it a degree of whiteness and opacity.
The milk is secreted after a full meal in larger proportion, than after a woman has fasted for some time.
In the latter case, the proportion of the expressed oil, coagulable matter, and sugar, likewise diminishes, and the milk contains besides these the neutral salts of the blood, and acquires a bitterness from the sebacious matter of the glands of the nipples.
In some women the milk always contains the salts of the blood, or the sebacious matter of the nipples.
The sebacious matter not only gives it a bitter taste, but also, sometimes, a yellowish colour and a thicker appearance.
The milk may contain any substance which is thrown into the stomach, and simply dissolved in water, without going through the digestive fermentations, and being converted into chyle.
The MUCUS.
IT covers the surfaces of the membranes that are exposed to any extraneous matter, such as the skin and internal membrane of the mouth, nose, lungs, aesophagus, stomach, intestines, urinary passages, &c.
It is a fluid of an adhesive viscidity approaching to a solid, and of greater viscidity in one part than in another.
It is a compound of a coagulable matter and water.
It is more or less viscid, according to the quantity of water with which it is combined.
It is of different degrees of viscidity in different parts of the body.
It will not combine with more water than what is already contained in it; neither can its viscidity be altered by digesting it with water, unless it begin to putrify; nor can the more viscid mucus of one part be converted into the less viscid of another.
If the water be evaporated from it by a gentle heat, the coagulable matter remains solid: if this be immersed in water, it will absorb that quantity which evaporated from it, but no more, and it will regain its former fluidity and viscidity.
It, for the most part, contains either no neutral salts, or so small a proportion as cannot easily be rendered sensible to experiment. It is colourless, insipid, inodorous, and incapable of stimulating.
It combines with concentrated vitriolic, nitrous, and muriatic acids, with concentrated solutions of some metallic salts, and also with concentrated or diluted solutions of caustic alkalies and caustic calcarious earth, into compounds soluble in, and diffusible through water.
Acids and some metallic salts dissolved in water, and concentrated, but not to that degree as to dissolve it, alcohol and aluminous salts coagulate it. It is also coagulable by the heat of boiling water, but not by a less degree of heat.
The mucus defends the membranes from being so much stimulated by any application as they would be, if they were not covered with it.
If the secretion be suddenly increased, the matter secreted is often a thin watery fluid containing the salts of the blood, and in consequence of them capable of stimulating; and the membranes are not defended from external applications.
If a greater secretion should continue than what naturally takes place, the mucus retains the salts, but often acquires a viscidity, and becomes incapable of being diffused through water: its colour also often grows white, greenish, or yellow; and now and then it acquires a smell.
The SALIVA.
IT is secreted by several glands in the mouth; and the principal part of it is thrown down into the stomach, to answer some purpose in the digestion of the food.
It is a fluid of an adhesive viscidity, with difficulty diffusible through water.
It consists of water, a coagulable matter similar to that of the mucus, and the salts of the blood, but not in so large a proportion as they are contained in the serum.
It contains a larger proportion of water than the mucus.
In its other properties it is similar to the mucus.
The PANCREATIC JUICE.
IT appears to be similar to the saliva, except that it is less viscid, and contains a larger proportion of the salts of the blood.
The saliva and pancreatic juice are probably watery menstrua for the solution of the food in the stomach and intestines, their viscidity preventing them from being absorbed before they produce that effect.
They have been said to act as ferments during the digestion; but as the fermentations of the stomach have never been made to take place out of it, we cannot judge of this by any experiment hitherto communicated to the public.
The BILE.
THE blood from which the bile is formed has probably gone through one circulation, without being exposed to the air in the lungs, or mixed with the fluids brought by the lymphatics from the different parts of the body.
The blood, from which the bile is formed, passes through the vessels of the abdominal viscera, before it arrives at the liver; but it does not take up any substance from them, or at least not in such a quantity as to be sensible to any experiment yet made; but, on the contrary, it appears perfectly similar in all sensible [Page 25]qualities to the blood returning by the veins from the other parts of the body.
There is no appearance of bile in the vena portarum of a living animal.
When bile in the jaundice is contained in the blood-vessels, it is secreted by all the secretory organs, and it is evidently contained in all the secretions.
The bile is formed from the blood in the secretory vessels of the liver.
It runs along the hepatic ducts into the ductus communis cholidochus, and from thence partly into the duodenum, and partly into the gall-bladder.
It continues for some time in the gall-bladder, and becomes more perfect in its properties there; from thence it returns into the ductus communis cholidochus, and passes into the duodenum.
The bile is a fluid of an oleaginous viscidity, consisting of a solution of a solid matter in water.
If the water be not evaporated from it, no alteration is produced on it by any heat between 32 and 112 degrees of Fahrenheits thermometer.
The bile is diffusible in any proportion of water.
If the water be evaporated from the solid part by a heat not exceeding 112 degrees of Fahrenheits thermometer, it is soluble in, and diffusible through, any quantity of water.
The solid matter of the bile melts if it be heated, and is decomposed if the heat be encreased.
If it is distilled by itself, it yields a larger proportion of empyreumatic oil than any of the other fluids, except the expressed oil and red part of the blood.
It is of a yellow colour, and a sweetish bitter taste.
When it is not combined with more water than it generally is in the gall-bladder, it does not putrify [Page 26]more readily than the blood; but if it be diluted with water or watery fluids, it putrifies more readily.
Acids and some of their compounds decompose it, and precipitate from it a resinous matter.
The acidity of the acid is lost by its combination with the other part; but if more acid be employed than what is necessary for the decomposition, the acidity of the superfluous quantity remains.
The matter precipitated has the peculiar smell of the animal.
It is solid in the heat of the atmosphere, melts in a moderate degree of heat, and burns very readily.
It is not soluble in water.
It is partly soluble in alcohol.
If the passage of the bile into the duodenum be stopt, acidities are apt to take place in the intestinal canal, the peristaltic motion does not go on properly, the faeces lose their peculiar colour and smell, and often acquire a more putrid foetor, and the digestion is hurt, but not entirely prevented.
The properties of the other secreted fluids have not been sufficiently investigated by experiments for us to be able to give any satisfactory account of them.
The CHEMICAL PROPERTIES of the ANIMAL SOLIDS.
THEY are a compound of coagulable matter and water.
They are naturally flexible; but, if the water be evaporated from them by a gentle heat, they become friable.
The water chemically combined, cannot be separated from them by expression. Exposed to about a red heat, they are decomposed; and if they be distilled by themselves, volatile alcali, empyreumatic oil, water, and calcareous earth, are formed.
When free from essential oil, blood, and the salts of the fluids, they are colourless, insipid, and inodorous.
They differ in their flexibility and elasticity.
Fibres and membranes are readily flexible, not capable of being broke by bending, and have a less degree of elasticity.
Cartilage is less flexible, capable in general of being broke by bending, and more elastic.
Cartilage often supplies the place of bone in young animals.
Heat, dilute acids, neutral saits, alcohol, metalic, and aluminous saits, astringent juices of vegetables, and several other substances, coagulate them, i. e. separate part of the water chemically combined, and of consequence contract them, diminish their flexibility, and harden them. Substances coagulating the animal solids, are called Astringents.
If they be exposed to a freezing cold, the water freezes; and upon thawing their texture is found to be altered.
Concentrated vitriolic, nitrous, and muriatic acids, caustic alkalis, even in a diluted solution, quick lime, and several of the metallic salts, combine with them into a substance diffusible through, or soluble in, water, and destroy their texture.
They are capable of putrefaction in the same manner as the animal fluids.
The GENERAL STRUCTURE of the BODY.
The BLOOD-VESSELS.
THERE are cavities in the body, called blood-vessels, in which the red part of the blood, the coagulable lymph, and part of the serum and superfluous water, are usually contained.
They consist of the heart, arteries, capillaries, and veins.
The heart consists essentially of two cavities, there being two hearts, properly speaking, joined, together in the human body, serving for two circulations of the blood; one through every part of the body, and one through the lungs.
The left side of the heart serves for the general circulation, and consists of two cavities, the auricle and the ventricle.
The auricle is a cavity which opens into the pulmonary veins at one end, and into the ventricle at the other. There is a valve placed at the opening into the ventricle, which prevents any fluid from passing from the ventricle into the auricle.
The auricle is in part covered with muscular fibres.
The ventricle is a cavity surrounded with muscular fibres, having one opening into the auricle, and another into a pipe, called the aorta or great artery.
At the opening into the aorta, there are valves, which prevent any fluid from passing from the aorta into the ventricle.
The aorta is a tube which begins at the heart, and dividing into several branches, goes to every part of the body.
It does not divide at once, but branches out as it passes along.
When it has arrived at any part, and divided into very small branches, these open into one another, so as to have a free and perfect communication every way: from these arise a smaller set of tubes, which also communicate in the same manner; and from them again arise a larger set, which have likewise a free communication.
The first set have been called capillary, or anastomosing arteries: the second have not got a name: the third have been called capillary veins; but I would term all of them capillary vessels.
From the third set arise tubes which terminate, in the heart, joining together as they go on towards it, and forming principally two large tubes, which open into the right auricle.
These are called veins.
The veins which are subject to frequent compression, from the action of the muscles, have valves which open towards the heart.
Each artery, capillary, and vein, is nearly cylindrical, but somewhat irregular in its diameter.
No muscular fibres appear on the arteries, capillaries, or veins in the human body.
These vessels are all of them, elastic, and capable of being distended, so as to contain a larger quantity of fluid than what is necessary to render them cylindrical.
Their elasticity is not sufficient to overcome the weight of their sides and keep them cylindrical, if [Page 31]they are not filled with a fluid, excepting in that part of the aorta nearest the heart.
When an animal is dead, and no chemical or mechanical change has taken place in the vessels, the elasticity is the same as when the animal was alive.
When an animal is dead, and the vessels act by their elasticity alone, they are incapable of contracting to half the size they are of at their utmost distention, supposing them to continue cylindrical.
When an animal is alive, the blood-vessels are always cylindrical, excepting when they are compressed by a considerable external force.
They are always full of blood.
When an animal is alive, the veins, capillaries, and small arteries, are sometimes contracted to less than half the size they are of at other times; therefore the veins, capillaries, and small arteries, in a living animal, have a contractile power independent of their elasticity, by which they adapt themselves to the blood, and continue cylindrical.
This power is similar to the muscular power.
When the vessels contain more blood they become longer, or their diameter is enlarged, or both; and, e contra,
When they contain less blood, they become shorter, or their diameter diminishes, or both.
The contractile power of the vessels is capable of diminishing either their length or diameter.
When an animal dies, the arteries and veins lose their cylindrical form, and are flattened, and the capillaries contain less blood in them.
The arteries, veins, and capillaries of a living animal, are commonly contracted to a greater degree than they can be by their elasticity.
The elasticity is commonly endeavouring to distend them.
If the vessels are emptied to such a degree that they cannot adapt themselves to the blood, and continue cylindrical, the animal dies.
The most essential effort of the living power, is, to adapt the vessels to the blood.
The COURSE of the CIRCULATION of the BLOOD.
THE blood passes from the left auricle of the heart into the left ventricle, from the left ventricle into the aorta, and from thence by the smaller arteries to the capillaries in every part of the body; from these it returns by the veins to the right auricle of the heart. The blood, for the most part, moves in one uniform direction in each artery, viz. from the heart towards the capillaries: it also moves in one uniform direction in each vein, viz. from the capillaries towards the heart; but although it moves in general from the arteries through the capillaries into the veins, yet its direction in any one capillary may be, and often is, altered and reversed.
Both the general velocity with which the blood moves through the whole system, and the proportional velocity of its motion in particular vessels, are constantly varying.
The POWERS producing the. CIRCULATION of the BLOOD.
THE force with which the blood moves in the veins, and the muscular contraction of the auricle, which takes place during the relaxation of the ventricle, propels the blood into the ventricle.
When a certain quantity of blood is propelled into the ventricle, its muscular fibres contract, being probably stimulated thereto by the blood.
This contraction of the muscular fibres of the right ventricle diminishes or obliterates it, and propels the whole, or part of the blood contained in it, into the aorta; the valve placed at the opening of the auricle into the ventricle, preventing its return into the auricle.
When the ventricle has emptied itself into the aorta, it relaxes and receives a fresh quantity of blood from the auricle; the blood being prevented from returning from the aorta by the valves placed at its opening into the heart.
The action of the heart tends to produce an equal and uniform circulation in every part of the body.
The CIRCULATION doth not depend on the ACTION of the HEART alone.
The circulation is not equal and uniform through the whole body, but the same quantity of blood flowing from the heart, a greater proportion of it sometimes circulates through one part, sometimes through another.
If the heart be the sole power propelling the blood forward, the circulation can only be increased in any one part by an increase in the size of the vessels, or removal of some obstruction to the circulation there, or a diminution of the size of the vessels, or obstructtion to the circulation in the rest of the body; and e contra the circulation can only be diminished in one part by a diminution of the size of the vessels, or obstruction to the circulation there, or an increase of the size of the vessels, or a removal of some obstructtion to the circulation in the other parts of the body.
The principal causes producing an alteration of the size of the vessels, or an obstruction to the circulation, are,
- 1st, An increase or diminution in the disposition to contraction in the capillary vessels, or in the external pressure.
- 2dly, The meeting of the streams of blood in the anastomosing vessels.
- 3dly, The attraction of the blood to the sides of the vessels.
The disposition to contraction in the capillaries of a particular part, or the external pressure, may be increased, so as actually to produce a diminution of the size of the vessels of that part, (notwithstanding the action of the heart,) and by consequence a diminution of the circulation of the blood in that part.
As the obstruction arising from the meeting of the streams of blood in the anastomosing vessels depends on the velocity with which it moves, it tends to render the circulation in a part equal, by preventing an increase or diminution of it.
As the blood is thoroughly mixed in the right ventricle of the heart, and is distributed from thence to the different parts, no alteration in its attraction to [Page 35]the sides of the vessels can produce an increase or diminution of the circulation in a particular part.
It has been supposed, that a viscidity in the fluids, or an increase of the size of their particles, often produced an obstruction to the circulation; but this opinion has not been proved, or rendered probable, by any experiment hitherto made public: oh the contrary, the red globules appear to be always nearly of the same size, except when they are broke down by putrefaction: the serum and coagulable lymph seldom or ever appear more viscid than when in their common state; and, if they were, their viscidity would affect the system equally.
The disposition to contraction in the capillary vessels, or the external pressure, may be so much diminished, as that the action of the heart continuing the same, the size of the vessels of a part may be increased, so as actually to occasion a greater circulation of blood in that part.
If the heart be the sole cause of the circulation, the only material alteration that could take place in the proportion of the circulation in the different parts, must depend on an increase or diminution of the disposition to contraction in the vessels, or on an alteration in the external pressure.
But the circulation may be increased in a particular part, the motion of the heart continuing the same, by causes which do not diminish the disposition to contraction of the vessels of that part, nor increase the disposition to contraction in the vessels in the other parts of the body, nor produce any effect on the external pressure.
Therefore the heart is not the sole power which propels the fluids through the part in which the circulation is thus increased.
The causes capable of increasing the circulation in a part, are generally such as tend to excite muscular motion, and are called stimuli.
Some part of the body, brought into action by these stimuli, is capable of increasing the circulation independent of the action of the heart.
The arteries are endowed with a muscular motion, by which they may increase the circulation in a particular part, or assist the heart in the general circulation of the blood.
The arteries at each contraction of the heart are distended; at each relaxation they contract.
This alternate contraction and dilatation might depend on their elasticity.
If their contractions and dilatations depended on their elasticity, their size at their utmost contraction in the living body should be equal to that produced by a fluid injected into them, with a force capable of overcoming the resistance the blood meets with in the capillary vessels, which, in the human body, is probably equal to eight feet perpendicular height of water.
But their size, even at their utmost state of dilatation, is less than that produced by a fluid injected into them, with a force equal to one foot perpendicular height of water, when the animal is dead.
Therefore their contractions and dilatations do not depend on their elasticity.
The additional force which occasions an increase of the circulation, in a particular part, must depend on the action of the arteries or capillaries.
As the capillaries do not contract and dilate alternately, and as the direction of the blood in any one [Page 37]of them is quite undetermined, this additional force cannot depend on the action of the capillaries.
If the arteries contracted and dilated by their elasticity, no additional force could be applied from their contraction and dilatation; since the heart would lose more force, in distending the arteries, than they would re-apply to the blood in contracting.
If the arteries, upon being distended by the blood thrown into them by the heart, are excited to a muscular contraction, and when they have performed this contraction relax, and like the ventricle of the heart, receive the blood easily into them, and when they are again distended, are excited to a second contraction, they may apply an additional force to that of the heart, so as to promote the circulation through the whole body.
If such contractions and dilatations be greater in any particular part, they will promote the circulation in that part; in as much as, when they are relaxed to a greater degree, they will suffer the blood to pass through them more readily into the capillaries; and, when they contract, they will empty themselves more thoroughly into the capillaries.
The arteries have a muscular contraction and dilatation, similar to that of the ventricles of the heart, by which they apply an additional power to that of the heart, so as to promote the general circulation through the whole body, and often to increase the proportional circulation in a particular part.
The motion of the blood is regulated by the action of the heart and arteries, and the contraction of the capillary vessels; and these arc measured by the pulse.
The PULSE.
| Indicates | by | It is called |
| 1st, THE strength of the contraction of the heart, | Strength, | Strong. |
| Weakness, | Weak. | |
| 2dly, The quantity of blood thrown out at each contraction, | Fulness, | Full. |
| Smallness, | Small. | |
| 3dly, The number of contractions, | Frequency, | Frequent. |
| Slowness, | Slow. | |
| 4thly, The regularity of its action, as to strength, quanity or frequency, | Regularity, | Regular. |
| Irregularity, | Irregular. | |
| Intermission, | Intermittent. | |
| 5thly, The strength of the action of the arteries, | Hardness, | Hard. |
| Softness, | Soft. | |
| Redoubling, | Redoubling. | |
| Trembling, | Trembling. | |
| 6thly, The irritability of the vessels, | Quickness, | Quick. |
| Regularity, | Regular. | |
| Slowness, | Slow. | |
| 7thly, The medium diameter of the arteries, | Dilatation, | Great. |
| Contraction, | Small. | |
| 8thly, The quantity of blood in the vessels, | Oppression, | Oppressed. |
| Smallness, | Empty. | |
| 9thly, The contraction of the capillaries, | Obstruction, | Obstructed. |
| Freedom, | Free. |
The STRUCTURE of the LUNGS.
THERE is a set of vessels in the lungs which contain air, and another which contain blood.
The AIR VESSELS.
The air vessels consist of a pipe, called the trachea; one end of which opens into the throat, and communicates with the amtosphere by the nostrils and mouth; the other divides into branches which go to every part of the lungs, and whose ends open into small cavities, or cells.
The air In the lungs is generally in motion; for either that which is at present contained in the cells, is passing through the trachea into the atmosphere, or a fresh parcel is passing from the external atmosphere through the trachea into the cells.
The whole of this motion is called respiration: when the air is passing in, it is called inspiration; when it is thrown out, expiration.
When the thorax is enlarged by the action of one set of its muscles, the pressure of the external atmosphere forces the air into the lungs; the other set of muscles which contract the thorax when put in action, force the air out of the lungs into the atmosphere. But the pressure of the atmosphere on the surface of the body counterbalancing its pressure on the surface of the lungs, neither the muscles of inspiration nor those of expiration are assisted or counteracted by it.
If the air continues at rest in the lungs for many minutes, or if a man continues to respire the same [Page 40]air, or if he breathes air that hath served for the inflammation of fuel or pure fixable air, he dies.
It is not determined whether pure inflammable air will serve for respiration.
Some vapours kill immediately if taken into the lungs, independent of their being unfit for respiration.
The BLOOD-VESSELS.
The [...] vessels of the lungs consist of two sets, viz.
- 1st, The Pulmonary.
- 2dly, The Bronchial.
The PULMONARY VESSELS.
The right side of the heart is similar to the left, excepting that both the auricle and ventricle have fewer muscular fibres, and that the auricle receives blood from the venae cavae, and the ventricle throws it into the pulmonary artery.
The pulmonary artery begins at the right ventricle of the heart, and goes from thence to every part of the lungs in the same manner that the aorta goes to every part of the body.
When the pulmonary artery hath divided into very small branches, these do not open into one another and form anastomosing vessels like the small branches of the aorta; but they join again, and form veins, which uniting together, go to the left auricle of the heart commonly in five trunks.
The CIRCULATION of the BLOOD through the PULMONARY VESSELS.
The blood passes from the right auricle into the right ventricle, from the right ventricle into the pulmonary artery, from the pulmonary artery into the pulmonary veins, and from the pulmonary veins into the left auricle,
The POWERS propelling the BLOOD through the LUNGS.
The muscular fibres of the right auricle contracting, propel part of the blood contained in it into the right ventricle, and they are assisted by the force with which the blood moves in the veins.
The muscular fibres of the right ventricle being stimulated to contract when it is full, propel part or the whole of the blood contained in it into the pulmonary artery, the blood being prevented from returning into the auricle by the valve placed at, the opening of the auricle into the ventricle.
After the ventricle has contracted, it relaxes and receives the blood from the auricle, it being prevented from returning from the pulmonary artery by the valves placed at the opening of the pulmonary artery into the ventricle.
The blood is thrown by the right ventricle through the pulmonary artery and veins into the left auricle.
Perhaps the pulmonary artery hath a muscular power, similar to the muscular power of the other arteries, by which it promotes the circulation of the blood through the lungs.
The blood meets with the same obstructions in its passage through the lungs that it does in its passage through the other parts of the body, excepting that there being no anastomosing vessels, there is no obstruction from the streams of the blood meeting in them, and opposing each others motion.
The blood meets with some additional obstructions in its passage through the pulmonary vessels, besides those it meets with in the other parts of the body, viz.
- 1st, The motion of the lungs in respiration, as there are no valves in the vessels, tends to retard the circulation, although the reverse hath been asserted.
- 2dly, If a sufficient quantity of respirable air be not received into, and thrown out of the lungs, the motion of the blood in the pulmonary vessels is considerably retarded.
The BRONCHIAL VESSELS.
An artery arises from the aorta, and spreads itself through the lungs, terminating in anastomosing capillary vessels, which open into veins in the same manner as the other branches of the aorta in other parts of the body.
The blood circulates in these vessels in the same manner as in the other vessels, arising from the aorta in other parts of the body.
The EXTRAVASATION and ABSORPTION of the LYMPH.
PART of the superfluous water and serum is continually passing through the sides of the vessels, particularly the capillaries, into the cellular membrane, and all the cavities of the body, so as to keep their surfaces moist.
It has been supposed that they passed through tubes appended to the sides of the blood-vessels; but such vessels have never been demonstrated, nor is there any reason for supposing that they exist, excepting in the glands.
The fluids, commonly extravasated, have been called the lymph.
It is uncertain whether it passes through the accidental pores in the sides of the vessels, or by cylindrical organised holes; but it is most probable that it passes through organised holes, as the secretion is regular and constant.
The pores or vessels it passes through, are called exhalants.
It is absorbed by the lymphatics.
A lymphatic is a tube nearly cylindrical, divided by valves, so at to have the resemblance of joints.
They arise from the cellular membrane, and cavities, and the greatest part of them go to the thoracic duct.
The valves allow the lymph to pass from the cavities to the thoracic duct, but prevent its passing from the thoracic duct to the cavities.
The lymphatics in passing from the cavities to the thoracic duct, go through the lymphatic glands.
The structure and use of these glands are not as yet ascertained.
The thoracic duct is a tube which begins near the diaphragm, and commonly terminates in the left subclavian vein.
At its opening into the left subclavian vein, there is a valve which allows the lymph to pass from it into the vein, but prevents the running of the blood from the vein into the thoracic duct.
Some of the lymphatics terminate in veins. These are similar in structure to those which terminate in the thoracic duct.
The POWERS producing the EXTRAVASATION and ABSORPTION of the LYMPH.
The contractile power of the blood-vessels squeezes the lymph into the cellular membrane and cavities.
The quantity thrown out is in proportion to the force of the circulation, the fluidity of the substances contained in the blood-vessels, or the quantity of the more fluid substances, and the degree of contraction of the capillaries and exhalants.
The joint of a lymphatic opening into a cavity, endeavours to fill itself from that cavity by its action as a capillary tube, the valves preventing the return of the lymph from the other part of the lymphatic. In like manner a lymphatic may fill itself entirely from the cavity in which it terminates, but its action as a capillary tube will not tend in the smallest degree to propel the lymph into the veins.
It is most probable that the joint of the lymphatic, next to the cavity, having absorbed a sufficient quantity [Page 45]of lymph to fill it, is stimulated to contract and propel the fluid into the next joint, and so on to the thoracic duct, or vein, in which it terminates; and having emptied itself, and being relaxed, it fills itself again from the cavity, and so continues to act: for there is apparently no other power in the body capable of producing a regular flow of the lymph through the lymphatics into the blood-vessels.
For in a living animal where the veins are contracting, and pressing the blood, if one end of a capillary tube terminate in a vein, and the other in a cavity; and if there be no action in that tube, excepting that which arises from its being a capillary one, or from the motion of the blood in the vein; if there be any motion in that tube after it is full, it will always be from the vein into the cavity, and never from the cavity into the vein, let the tube be of any size or shape whatever.
Further; the alternate pressure of the lymphatics arising from the alternate contractions and relaxations of the blood-vessels, or muscles, is not sufficiently powerful, universal, or equal, to produce a regular flow of the lymph through the lymphatics into the blood-vessels.
Neither does the cellular membrane and cavities force the lymph into the lymphatics, and through them into the veins.
The extravasation of fluids from the blood-vessels in to the cellular membrane and cavities, and their reabsorption, generally take place in the above manner.
Sometimes the coagulable lymph is thrown out by the exhalants.
When the coagulable lymph is thrown out, it most commonly coagulates.
If it coagulate, it cannot be taken up by the lymhatics, till it be redissolved.
In many cases it redissolves, and is absorbed much sooner than it can be rendered soluble in water, by putrefaction when out of the body. At other times it continues in the cavity for many years.
The red part of the blood is also sometimes thrown out by the exhalants. In this case, its particles are broke down probably by the first stage of putrefaction, and it is afterwards reabsorbed.
The same things may happen, if the red particles and coagulable lymph are extravasated in consequence of the rupture of a blood-vessel.
In particular parts, as in the corpora cavernosa penis, the extravasation and absorption is probably performed in a different manner, and by different vessels.
All absorbent vessels must have a power of propelling the fluids into the blood-vessels, sufficient to overcome the force of their contraction, by which they endeavour to propel the blood out of any opening.
The HEAT of the HUMAN BODY.
THE bodies of quadrupeds have a disposition to maintain the same degree of heat nearly.
The heat of quadrupeds of the same species is generally the same, especially in mankind.
The common heat of the human body in health, is ninety-eight degrees of Fahrenheit's thermometer.
The heat is the same throughout the whole body, excepting that a cold substance applied to the skin diminishes its heat; and the heat of the blood, flowing from a vein in an extremity that is exposed to a cold atmosphere, is reduced two or three degrees.
Otherwise the heat continues the same, whether that of the atmosphere, or other surrounding bodies, be greater or less than ninety-eight degrees, unless when it produces a disease; the consequence of which is an increase or diminution of the heat of the body.
The body is capable of resisting different degrees of external heat or cold, according to the habit it has acquired. There are instances of its bearing 20 degrees below 0 of Fahrenheit's thermometer, with very moderate cloathing, and 115° above, without alteration.
The heat may be increased or diminished by alterations in the body itself, especially in diseases.
The heat has seldom been observed to be less than ninety-four, or more than a hundred and ten degrees of Fahrenheit's thermometer.
An increased action of the living power in any part, or in the whole body, increases the heat; and e contra; a diminution of the action of the living power, diminishes the heat either in quantity or degree.
Fluids rubbing against solids, or very small particles of a solid immersed in a fluid rubbing against one another, or against a solid, produce no sensible heat; therefore neither the friction of the blood against the vessels, nor the friction of the red particles against one another, or against the vessels, produces, maintains, or regulates the heat of the body.
It has not been proved, by any experiment hitherto made public, that the fermentations producing, or destroying the fluids, generate heat; and if it were, these fermentations do not go on so regularly, universally, or constantly, as to produce, maintain, or regulate the heat of the body.
The heat is not at all proportion to the evaporation, as a double quantity evaporated by the insensible perspiration, makes no alteration in the heat.
The power which produces, maintains, and regulates the heat of the human body in health, produces heat when the surrounding substances are heated to a less degree than 98 of Fahrenheit's thermometer, and cold, when they are heated to a greater degree.
The NERVOUS SYSTEM.
THE brain is a soft mass, internally of a white colour; externally of a greyish or ash colour.
It is furnished with blood-vessels in the same manner as the other parts; excepting that larger arteries anastomose, and the smaller veins enter more suddenly into a large trunk, whose sides are of a firmer texture.
In quadrupeds it is contained in the cavity of the head.
In man it is in a larger proportion to the whole body, than in any other quadruped, or any bird or fish hitherto known.
From the white part masses of fibres arise, which go to every part of the body. These are called nerves.
One large mass passes down through the cavity of the spine, and is called the spinal marrow.
A little of the cineritious part, is contained in the middle of this, and also in the optic nerves.
The brain, spinal marrow, and nerves, are covered with membranes of a much firmer texture.
The nerves proceed from the brain in trunks, which branch out as they pass to the different part, of the body.
Upon examining the trunks with a microscope, they appear to consist of very small fibres, which are only separated from one another in the branching.
In their passage they sometimes join again, forming roundish masses called ganglions, from whence they proceed to the different parts.
When they divide into very small branches, they have been supposed to become softer, and seem to go to every the smallest part.
The SENSIBILITY, MOBILITY, and IRRITABILITY of the BODY.
THE sensibility is a property of the body, by which external substances applied to it, excite sensations in the mind.
The mobility is an original power of motion, by which certain parts of the body are capable of moving themselves without any external motion imprest.
The Irritability is a property of the body, by which external applications to particular parts excite a motion in the moveable parts, independent of the motion imprest.
These properties depend on the brain and nerves.
The SENSIBILITY.
The sensibility depends entirely on a part's being connected with the brain by the nerves; for,
If the nerves going to any part be cut through, the sensibility is lost.
If the nerves going to any part be moderately comprest, the sensibility is diminished.
If the nerves be comprest strongly, the sensibility is lost.
If the pressure be soon removed, the sensibility recurs.
If the pressure be continued for a long time before it is removed, the sensibility returns more slowly, or not at all.
Pressure on the brain, diminishes the sensibility of the whole body.
If a small branch of a nerve be cut through, so as to take off the sensibility of a part of the skin, it may be restored in time.
The sensibility may be impaired, or lost, without any sensible pressure on the nerve, or alteration of its structure.
When there is no wound in the body, the sensations appear to be in the place where the application exciting them is made.
If an extremity be cut off, an application made to the stump, may produce sensations which appear to be in the part amputated.
Can a sensation be excited apparently in a part by an affection of the nerve going to it, the body being whole?
Every part of the body is capable of sensation in a sound or morbid state.
The bones and cartilages do not appear to be sensible in a sound state, whatever application be made to them; but in a morbid one they may become sensible.
All the other parts of the body appear to be sensible in a sound state; for the distention of a part considerably beyond its present disposition to contract, either by its muscular power or elasticity, is capable of exciting sensations in every other part of the body.
There are applications, which are capable of exciting sensations in one part, that produce no such effect in another.
Some of the sensible parts are only capable of sensation from distention in a sound state, such as the membranes.
One part may be sensible to an application which another is not, and the second part may be sensible [Page 52]to another application, which the first is not; as the effluvia of musk do not affect the eyes, although they affect the nostrils, and the rays of light affect the eyes, but not the nostrils.
Some parts of the body are only capable of the sensation of pain; others are capable of various sensations, of which pain is always one.
Some applications are capable of exciting pain only; others may excite various sensations.
Every sensation excited in a very great degree, is painful, and several are also painful from being very weak.
Those parts of the body, which are capable of a veriety of sensations, are generally called the organs of the senses. These are,
The skin, the mouth, the nostrils, the eyes, the ears; the stomach is capable of several sensations besides pain, but not of so great a variety as the organs of the senses.
Some other parts of the body are also capable of some sensations not painful.
All the sensible parts may have their sensibility increased or diminished.
The MOBILITY and IRRITABILITY.
Part capable of original motion, are called the moving parts.
In many of the parts capable of original motion, there are red fibres called muscular fibres.
In some of the parts capable of original motion, no such fibres have hitherto been demonstrated.
All the parts of the body are not capable of original motion.
The muscles, blood-vessels, lymphatics, secretories of the glands, and skin, are capable of original motion.
The moving parts are capable of contracting beyond that degree of contraction which would arise from their elasticity.
All the actions of the body, and all the power which it exerts, depend upon the contraction of the moving parts.
When a muscular fibre, or any other moving part, continues in action for a considerable time, it does not, in general, exert one continued contraction, but a number of alternate contractions and relaxations. The relaxations, when the body is strong, or the whole strength is not exerted, are often hardly distinguishable; but when the habit is weak, or the whole force exerted, they become very apparent.
A contraction may however probably continue for a very long time, without any intermediate relaxation, as in a spasm.
When any motion takes place in consequence of a relaxation, it is from the elasticity or weight of the part, or from some external power.
The original motions are produced by volition ideas of the mind, or certain external applications, called stimuli.
There must be the same intercourse, which is necessary for sensation, between the moving part, and the brain, by means of the nerves, to render volition capable of exciting a motion in it.
Many of the moveable parts are incapable of being put in motion by the will.
An idea of the mind may excite a motion independent of, and contrary to the will, provided the part be connected with the brain by the nerves, as for sensation.
The will may acquire a power over a moving part, which it could not affect originally.
The motions excited by the will are called voluntary motions; those excited by ideas, or stimuli, independent of, or contrary to the will, are called involuntary.
All the parts of the human body, capable of voluntary motions, have red muscular fibres.
The will and ideas are both capable of producing contractions and relaxations in the moving parts.
If the communication between the brain and a moving and irritable part, be cut off by cutting thro' the nerve, a motion may be still excited in it by a stimulus; hence stimuli may excite motion without affecting the brain, and therefore all the motions excited by them, are not begun in the brain, and carried along the nerves to the moving part.
If a nerve be cut through, so as to leave a portion of it adhering to a moving part, a stimulus applied to the nerve, may excite a motion in the moving part. Hence, the action of a nerve upon a part, may excite a motion in it; and the motions excited by the nerves, do not all arise in the brain.
If the communication between the brain and a moving part by the nerves continues, a stimulus applied to the brain may excite a contraction of the moving part.
The motions produced by the application of stimuli to moving and irritable parts are apparently the same, whether the part be connected with the brain by the nerves, or not; excepting that the motions excited, become more languid after the moving part has been separated some time from the brain, and at last the power of motion in it is entirely lost.
The same things are true of the motions excited by the application of stimuli to the nerves going to a moving part.
Hence, it is probable, that the motions excited by the application of stimuli to a moving and irritable part, or to the nerve going to a moving part, do not arise in the brain, but immediately in the nerves, or in the part; the brain in this case only keeping up the life of the part, and rendering it capable of motion.
When a stimulus produces a contraction in a moving fibre, the force of that contraction is often far greater than the force with which the stimulus was applied. Therefore, when a stimulus excites a motion, it is not in consequence of a communication of the power employed in applying that stimulus: nay, the motion may be the very reverse of that which would have been produced by the exertion of that power.
When a stimulus applied to a nerve produces a contraction in a moving fibre, it is a question whether the motion is excited in the nerve, and communicated to the fibre, or produced immediately in the fibre, without any motions being excited in the nerve; for in this last there is often no apparent motion excited.
It has been conjectured by some, that the motion was communicated by a fluid flowing through the nerves as tubes; by others, that it was communicated by vibrations; and by others, that it arises from an elastic vapour surrounding the nerves: but none of these conjectures are founded on experiment, neither are any of them any ways capable of accounting for the appearances.
As the influence of a stimulus on a moving fibre is not occasioned by any mechanical communication of motion, may not a stimulus applied to a nerve, exert its influence on a contractile fibre, without any [Page 56]mechanical communication by any motion running along the nerve.
If the brain is not diseased, and two parts of the body communicate with it by the nerves, as for sensation, an application made to one of these parts may excite a contraction or relaxation in the other, although none of the substance applied, be carried from the one to the other, and although no sensation be excited by the stimulus. Hence a medicine applied to one part of the body, may produce an effect upon another, although none of that medicine be carried to the part on which that effect is produced.
The effect of an application upon a part at a distance from that where it is made, may be the same which it would have produced if applied to that part; or it may be the reverse, or totally unconnected with it.
Quer. May not the application in this case influence the distant part, without any communication from a mechanical motion running along the nerves of the one part to the brain, and from the brain by the nerves to the other part?
An application to one part, may produce a motion in another, although it would have had no effect, if it had been made to the part itself
A stimulus applied to a part incapable of original motion, may excite a motion in a moving part at a distance.
If the communication between the brain and any part of the body, by means of the nerves, be cut off, applications made to that part, will not affect the other parts, nor will applications to the other parts, produce motions in that; unless the nerves be cut off from a muscle, whose fibres have been accustomed to contract at one and the same time, such as the heart. [Page 57]In that case, if you stimulate one of these fibres, the whole are brought into immediate contraction; those not stimulated, contract, to all appearance, as soon as the one to which the stimulus is applied.
As in this case the communication between the fibres by the nerves is cut off, and as after cutting thro' the nerves of a small part of the body, the sensation may in time be restored, is there not a communication of nervous influence, between the parts that are in contact, independent of the nerves?
The parts on which stimuli are capable of acting so as to produce motion, are called the irritable parts.
All the parts of the body are irritable in a sound state, excepting the bones, cartilages, and tendons.
All the parts of the body may become irritable in a morbid state.
Stimuli may produce motion in a distant part, when applied to a part incapable of original motion; or, in other words, all the irritable parts are not moving parts.
An application that produces relaxation, or diminishes contraction, is called a sedative.
A substance may act on one part as a stimulant, on another as a sedative.
A substance may act on one part as a stimulant or sedative, and have a lest effect, or none at all, when applied to another, although otherwise equally irritable. Such stimuli are called specific.
There are some parts upon which stimuli in general produce greater effects than they do upon others.
A greater number of substances act also upon these parts.
The membranes, ligaments, and blood-vessels, excepting the heart, are incapable of being affected by any other stimulus but distention.
Some of the applications capable of affecting the moving parts, tend to destroy the fibres by mechanical or chemical effects; some of them have no mechanical or chemical power of action.
The irritability and mobility of a part may be increased, diminished, or entirely lost.
CUSTOM and HABIT.
CUSTOM is the frequent repetition of any application to the body, capable of affecting the sensible or irritable parts, or it is the repetition of any action or motion of the body.
Habit is the effect of such repetition.
An application, producing a sensation, may have its power increased or diminished by custom.
If the mind pays particular attention to any impression, its force and distinctness is increased. Hence arises the improvement of the eye, ear, &c. in distinguishing objects in painting, tones in music, &c.
If the impressions are very strong, so as to excite great attention, their force is increased.
If the impressions are not attended to, their force is diminished. Hence after living for some time near any thing producing a great noise, the noise is hardly heard.
The power of the will, in producing motion, may be increased by custom, and diminished by disuse.
The will, in frequently producing a motion, may not only have its power increased, but it is also capable of producing that motion with greater accuracy, and by frequent attempts may acquire a power over a moving part, upon which it has naturally little or no influence.
A motion may arise from a volition in consequence of custom, which was not naturally connected with it; as a man in turning in a loom does not will the motion of his hand, but of the end of the chizel.
Quer. Can a man produce two distinct motions by his will at once; or, when two distinct motions are produced, does the will produce them successively? The impression arising from one volition remaining till the mind renews it, after having produced the other, in the same manner as the impression of a flame making a circular motion, remains on the eye, so as to give an idea of a compleat circle.
The power of producing two distinct motions, apparently at the same time, is greatly increased by custom.
From the above circumstances the facility of execution acquired by custom arises.
The power of an idea in exciting motion, may be increased or diminished by custom.
An idea strongly imprest on the mind, is for the most part more powerful in exciting a motion, than one weakly imprest.
The power of an application in impressing an idea, may be increased or diminished by custom, as is above described, and of consequence the power of an idea in exciting motion.
Supposing the impression on the mind the same, if an idea has frequently produced a motion, its power [Page 60]is increased. On the contrary, if in idea has been often excited, and if the motion depending upon it has by any means been prevented, its power is diminished, or lost.
The action of an application producing, diminishing, or altering the mode of, contraction of a moving part, and which at the same time has no effect on the mind, may be increased or diminished by custom.
If it be often applied, so as always to produce its effect, its power, or the certainty of its action, is for the most part increased.
An application of an equal apparent force does not always produce the same effect. If the same quantity of ipecacuhan be twice exhibited at the interval of several days, it may vomit at the first exhibition, and not at the second; or it may produce vomiting at the second exhibition, and not at the first.
In applying medicines, which do not act as simple stimuli, their particular effect cannot be increased by increasing the dose, they being converted, into simple stimuli. Thus small doses of saccharum saturni produce costiveness, but a very large dose frequently purges.
An application frequently repeated, so as to produce its proper effect, often becomes more constant and uniform in its action, although it may become necessary that it should be applied in a greater degree.
If an evacuating medicine be repeatedly exhibited, it generally requires a larger dose at the second, and some of the subsequent exhibitions, to produce the same effect as the first; but if these produce the effect, the power of the medicine is afterwards increased.
The more violent the effect of any application, the more is its power increased by repetition.
If an application be made in so small a degree, as not to produce any effect, or if its effects are by any means counteracted, its power is diminished or lost.
The repeated application of some medicines in any circumstance diminishes their powers.
All the natural powers of action in the body are increased by frequent exertion.
If two or more fibres have been accustomed to contract together, either by the action of the will, by an idea, or by stimuli; or if the contraction in one of them be produced by the will, while the other is brought into action at the same time by a stimulus, the producing of a contraction in the one by an application to it alone, will produce a contraction in the other. If they be fibres of the same muscle, and acted upon by a stimulus, this will happen after the communication with the brain by the nerves is cut off, but not otherwise.
If, after this habit is acquired, one of these fibres is made to contract frequently, while the other is prevented from contracting, the habit is lost or destroyed.
If any motion, or state of the body, be repeated at a particular period of time, it will often return at that period, although no other cause be applied but the habit acquired.
A habit may be destroyed by counteracting and preventing its effects.
Two habits may be so connected, that preventing the one from taking place, may prevent the effects of the other.
Custom has also a powerful influence on the mind.
EXERCISE, REST, SLEEP.
WHEN a moving part is brought into action by the will, an idea, or stimulus, that action sometimes ceases upon removing the cause, sometimes it continues after the cause is removed. This last frequently happens in the production of diseases.
When it is necessary for the continuation of an action, that its cause should be continually or repeatedly applied, the original power seems gradually to be exhausted, so that the motions for the most part become gradually weaker, and at last are not to be produced, as in the case of exercise.
There are some actions which are necessary for life, that are continued by the application of stimuli, and nevertheless do not exhaust the original power; such as the action of the heart, the peristaltic motion of the intestines, &c.
If these actions are increased beyond their common pitch, or beyond what can be allowed by the present strength of the system, they also exhaust the original power.
A great exertion of the faculties of the mind also, exhausts its powers.
Rest restores both to the body and mind their powers of action
In perfect sleep, both the body and mind are at rest, excepting in those particulars where an exertion is necessary to life. These exertions are in the alternate contractions of the heart and arteries, the motion of the muscles in respiration, the tone of the muscular fibres, blood-vessels, and other moving parts, the action of the lymphatics and excretory ducts, the peristaltic motion of the intestines, &c.
The common exertions of the body and mind, when a man is awake, exhaust to such a degree, as to require that rest which is found in sleep to allow the original power to recruit itself.
In sleep the mind is often brought into action, sometimes from affections of its own, sometimes from affections of the body. The body also exerts other powers besides those necessary for life. In these cases the original power is less recruited, and that in proportion to the exertion.
Although the original power may be so far exhausted as to require to be recruited by sleep, that state may nevertheless be prevented by any thing exciting great attention of the mind, by applications to the body producing uneasiness or pain, or by an increased action of any of its parts, or by any action or contraction which continues after its cause is removed.
The same causes may render sleep less perfect, although not sufficient to prevent it altogether.
Although rest is not compleat at the beginning of sleep, it has a tendency to become so during this state of the body. In particular, all actions and contractions remaining after their cause has been removed, are apt to go off.
During sleep the original power appears to be so much accumulated, as to give a disposition to action, both to the mind and body, from the slightest cause, and this state of the body goes off of course.
At the beginning of sleep, the rest is generally less perfect; it becomes gradually more so for a certain time afterwards. When the original power is recruited, the mind begins to be put in action, and at last the whole system, at which time sleep goes off.
A continued or strong action of one part of the body, may not only exhaust the original power in that part, but also in all the others.
A great exertion of the powers of the body, may exhaust the powers of die mind, and é contra, a great exertion of the powers of the mind, may exhaust those of the body.
A frequent exertion of the original power in one part of the body, tends to strengthen that part, but to weaken the other.
An exertion of the original power, increases the loss of fluids, and renders a greater quantity of food necessary. Hence animals that require a considerable quantity of nourishment when awake, may sleep for several months without any being taken in.
A loss of fluids generally increases the powers of digestion, excepting when they are disordered by disease.
A moderate exertion of the powers of the body, in proportion to the present strength, powers of digestion, food, and sleep, tends to strengthen the whole body.
A violent or continued exertion of the original power, if it be not recruited by food and sleep, may weaken to that degree as to kill.
A repeated exertion of the powers of the mind, tends to strengthen its faculties; but at the same time to weaken the original power in the body.
Unless the body be endowed with a certain degree of strength, the mind cannot exert itself powerfully.
Exercise of the powers of the body, tends to weaken the mind, except so far as is necessary to give the body the proper strength.
But a moderate exercise of the body and mind together, tends to strengthen the whole system, so that by custom the original power in the whole may be increased.