8 ^:^&>$ | ARMED FORCES MEDICAL LIBRARY [ | Washington, D. C. L________________________________I A CHEMICO-PHYSIOLOGICAL ESSAY, DISPROVING THE EXISTENCE OF AN iERIFORM FUNCTION IN THE SKIN, AND POINTING OUT, BY EXPERIMENT, THE IMPROPRIETY OF ASCRIBING ABSORPTION TO THE EXTERNAL SURFACE OF THE HUMAN BODY. By JOSEPH KLAPP, OF A LB ANT, NEW-TOR K, HONORARY MEMBER OF THE PHILADELPHIA MEDICAL SOCIETY. "Fiat Experimentum." ,"' ,'•,.:„ ?,-.-', .7--. PHILADELPHIA: fe^c ?^ PRINTED FOR THE AUTHOR, BY JOHN H. OSWAL 1805. D -^'V. AN INAUGURAL ESSAY, FOR THE DEGREE OF DOCTOR OF MEDICINE, SUBMITTED TO THE EXAMINATION OF THE REV. JOHN ANDREWS, D. D. PROVOST, (Pro Tern.) THE TRUSTEES AND MEDICAL FACULTY OF THE UXIVERSITY OF PILYA~S\ LVAjVLJ. ON THE 3d DAY OF JUNE, 1805. 3W4i fay StoefcC'Witv-. f'iii 11? £*ttMfc *f W V-fr TijiJ !.)ii < ,Mt In -..I ■■••I. fe »on>; rtU'JiJd Jtl I INTRODUCTION. XJl favorite author, not less distinguished for literary ac- complishments, than correctness of observation, says, a compo- sition that enters the world with a view of improving it, has a claim to the utmost indulgence, though it fail of the effect in- tended. If such encouraging lenity await the voluntary writer, whose object to instruct is often alloyed by an indignant thirst for public adulation, my claims on the score of indulgence can- not but meet with liberal success, as nothing less urgent than a law of the University could have induced me, at this juvenile period of my life, to appear in the character of an author. The subject which has been selected for this essay, is one which has been much canvassed by men of acknowledged ta- lents ; many of the difficulties, however, attending its satisfac- tory investigation, were either left neglected, or imperfectly sur. mounted, though it for a while attracted the experimental at- tention of a Cruikshank, a Priestley, and an Abernethy. The present enlightened state of medical science excepts none from the privilege of laboring in her enchanting dominion ; and as invaluable truth is alike appreciated, whether detected by the searching penetration of irresistible genius, or discover- ed by the good fortune of a mere novice in medicine, I have been induced to venture on the subject under consideration, without pausing to offer an apology for interfering with the la. hours and opinions of such eminent characters. ..............................................and truth alone, S/iall be our chosen theme, our glory to the last. Cowpmr, Xll The theoretical and practical advantages derived from a cor- rect knowledge of the laws and operations of the animal body, are too generally valued, to require commendation, and the per- nicious tendency of ascribing functions to parts not recognised by the ceconomy of nature must be evident to every leader. When we recollect that just ideas of the nature and cure of disease, cannot be obtained without the aid of physiological in- struction, the necessity of cultivating this important branch of our science with nicety and carefulness will occur to the most of observants, and the often unfortunate consequences of mis- taken publications cannot be exemplified in a more striking manner than a candid disclosure of the error in which I was nearly involved. The transpiration and absorption of the gases by the skin, as apparently demonstrated by authors of unquestionable integrity and reputation in medicine, have for some time past engaged my consideration, and so firmly did I believe in their proofs and -? observations, that a series of experiments were actually institut. ed to ascertain the influence and connection of these functions with the pulmonary forms of fever. But the result of a few of their most interesting experiments carefully repeated, gave me reasons to believe that there was some fallacy in the case, and a further enquiry, which was then anxiously carried on, soon confirmed my suspicions. The experiments which constitute the basis of this essay were conducted without any preconceived notions which could bias their natural import, and the fidelity with which they are de- tailed, can be attested by a few ingenious friends who had the goodness to assist me in their performance : but how far they will go to effect a decision on the subject, I leave to be determin- ed, with all due deference, to the better judgment of those who may hereafter give them an attentive examination. mjjiauw—wwbtmium 111 amr:wsma AN INAUGURAL ESSAY, Disproving the existence of an ariform func- tion in the Skin, &c. PART I. PHYSIOLOGISTS have long laboured with diligence to discover the functions of the Skin. The insensible emanations from its surface were known to Galen; and the great Sanctorius proved, in his statical expe- riments, that they consisted of watery vapour, endowed with certain excrementitious qualities. Since the days, however, of these two celebrated Physicians, new researches have been made, and many of which have end- ed in imputing to this organ a more important office in the ani- mal body. Count De Milly recorded a paper in the memoirs of the Royal Academy of Sciences, at Berlin, in the year 1777, in which he adduces experiments in proof of the discovery of an elastic fluid which passes off by the Skin. The imperfect man. ner in which experimental enquiries were conducted at this pe- riod of physiological improvements, necessarily connected with chemical knowledge, give? many reasons for believing that the Count was mistaken j particularly, when it appears, from the experiments of a judicious and more modern writer,* that no * Abemethy. ( 14 ) correct inference can be drawn, of the triform function of the Skin from the analysis of gases collected, unless they were first received over quicksilver. Count De Milly says, being in a warm bath, half a pint of air might have been collected over the water, in the space of three hours ; and from his analysis, which was both inaccurate and very incomplete, says an au- thor * in Nicholson's Journal, he concluded it was carbonic a- cid gas. Two years subsequent to the publication of the above me- moir, Mr. Cruikshank, an ingenious Physiologist of England, gave to the world an essay on insensible perspiration. His object being chiefly to investigate the quality of the watery va- pour emitted by the Skin, much information on the ariform discharge could not be expected. The following experiment, however, I will take the liberty of detailing, as the only one, in his publication, that relates to our subject. He introduced his foot, previously washed and dried, into an empty bottle, excluding the access of external air by means of a moistened bladder ; after retaining it in this situa- tion for one hour, he withdrew it, " the fluid collected" says he,, " produced no change on the lime water, but lime water thrown into the bottle and agitated became as turbid as when the air in which the wax taper had extinguished hself, was mixed with it. "This last experiment" continues Mr. Cruikshank " I re- peated several times and with the same success ; from this I inferred, that admitting the common theory of fixed air and Phlogiston, something passed off with the vapour of insensible perspiration of the skin which rendered air fixed." Inductions from incorrect data have always been fruitful sources of error in medical philosophy. This experiment, for two good reasons, cannot authorise the conclusion which Mr. Cruikshank has de- duced; first, because a moistened bladder will, by furnishing car- bon to the oxygenous portion of the air in the bottle, yield fixed * Trouaset. ( 15 ) air ; and secondly, because lime water poured out of one bottle into another, with the addition of agitation, will become turbid, from the chemical union of the carbonic acid of the atmosphere with the calcareous earth, as any one will find by making the experiment. Doctor Ingenhouz, about this time, paid some attention to the nature of the bubbles of air which he saw arise from the skin while immersed in water; but his experiments are few, and are liable to many objections that apply to De Milly's and others who have not taken the necessary precaution of ascertaining the nature of the gases contained in the water in which their ex- periments were made. Mr. Trousset, a French Physiologist, has published an ac- count of his experiments made in water, in which the transpi- ration of carbonic acid gas is denied, but the emission of azotic air by the skin is contended for. That gases are disengaged from the surface of the body, while immersed in common water, no one will pretend to deny ; but that they are prepared in the body, and emitted by minute vessels which open on the skin, is fully refuted by all the expe- riments detailed in the sequel of this Essay. If then, the air collected, does not come from the vessels of the skin, we must look to the water as the only source which can, under these cir- cumstances, yield it. As plants, under the influence of solar light, will readily dis- engage from pump-water, and the most of other waters in which they are placed, a considerable quantity of pure air, and as Professor Woodhouse has clearly proved, from a number of decisive experiments, that it is produced by the decomposition of carbonic acid with which the water is impregnated, I may conclude that the generality of waters contain fixed air; and that waters are more or less impregnated with azotic air, ac- cording to local circumstances, is now too well ascertained, to ( 16 ) be disputed by any one. With these considerations, found- ed upon incontrovertible truth, I do not hesitate to determine, in my own mind, that the evolved heat of the hand, foot, or of the whole body, which were the subjects of experiments under the direction of different Physiologists, expanded the gases contained in the water which they used, and thus caused them to rise in bubbles of air from the surface of the skin. This conclusion is rendered more probable, when we recollect the experiments which have long since been'made by Dr. Priestley in water exhausted of all its air, in which not a single bubble of any gas whatever was seen to arise, though the skin was immersed in it for a considerable time. The Doctor expressly declares, that the perspiration of ani- mals does not contaminate common air as the process of respiration does. I am well aware it is asserted that water absorbs carbonic acid as fast as it is emitted by the pores of the skin, and that this circumstance accounts for the result of the experiments alluded to. But to this I ask leave to reply, in the first place, that fixed air does not so rapidly unite with water as to preclude an opportunity of detecting it, if any were thrown out; and in the second place, that this objection does not apply to this mode of experimenting to discover whether azotic air is ever thrown out in perspiration, as many Physiologists assert ; and as they have erred in one instance, it is more than provable, from what has already been advanced, that neither, carbonic acid nor azotic air, is ever thrown out in the perspiration of animals. But what renders the explanation which I have given, of the origin of the gases collected over water, in which the. hand or the whole body were immersed, still more satisfactory, is the simple, though not less conclusive experiment which was made, by holding my hand and forearm, [previously invested by var- nished silk which was impervious to air} in a tub of pump wa- ter : in a short time innumerable sphericles of air were seen? ( 17 ) both by my friend and myself, to form on the external surface of the silk, and gradually rise to the top of the water. The successive formation and disengagement of minute bub- bles of air, being always confined to the surface of the skin, while immersed in water, and not proceeding from portions of water remote from its surface, may be urged as an argument in favor of gaseous transpiration ; but error, from this quarter, would be too palpable, to elude detection ; vegetables, while im- mersed in water impregnated with carbonic acid, and exposed to the light of the sun, disengage bubbles of pure air from the surface of their leaves ; yet who will contend that it comes from their fibrous texture ? In my humble opinion, the disengaged heat of the skin enables us to explain, as clearly, the one fact, as the decomposition of fixed air does that of the other. The embarrassment in which many Physiologists have in- volved themselves, on the interesting subject of the functions of the skin, I regard as similar, in many of its concomitants, to the once prevalent, though erroneous opinion, that vegetables purify atmospheric air, by absorbing its azotic, and perspiring its oxygenous portions. ThiB opinion, however, by the light of modern discoveries, has been exploded, as an unhappy hypo- thesis, originating out of incomplete researches ; and for an ex- planation of the source of the air disengaged by healthy plants, under water, we are very justly referred to the previous condi- tion of this fluid. Mr. Abemethy, a practical physiologist, and surgeon, of London, published in the year 1793, an essay on the functions of tire skin, in which he maintains, by a variety of experiments, that not only fixed air and azotic gas are thrown out by the skin; but that oxygen air and carbonic acid gas are very readily im- bibed ; whilst the nitrous, hydrogenous and nitrogenous gases tardilv gain admittance into the absorbing vessels. I do not c: C 18 ) think it necessary to detail, in particular, the experiments which Mr. Abernethy performed, but will mention that the chief of them were made by holding his hand and wrist in an inverted glass vessel, and in a medium of different gases con- fined over mercury. He also made two or three experiments in water, but in these he could not discover that carbonic acid gas was emitted by the skin ; believing that the water absorbed the gas, he soon discontinued this mode of prosecuting his subject. M. Seguin, in 1792, delivered a paper on the functions of the skin, to the Royal Academy of Sciences, at Paris. The ac- curacy and precision with which this philosopher conducted his experiments, have never been questioned; yet it is well known, tl\at they afford a result entirely different from those of Mr. Abernethy. M. Seguin, satisfactorily proved, in his pa- per, by a great number of ingenious experiments, that the skin, with its cuticle entire, absorbed neither air nor water. Mr. Fourcroy declares, that " it is not true that there pass off, through the skin, as some moderns have asserted, elastiq fluids, and especially carbonic acid gas." After having adduced the above respectable authority in be- half of the sentiments which are laid down in this essay, I will first venture a few observations, founded on anatomical and physiological knowledge, pointing out the improbability of an triform function in the skin, and then proceed to detail the ex- periments which fully authorise my disbelief in such an opera- tion. In the very commencement of this undertaking, I am met by a conviction of being incapable of rendering that justice to truth, which is requisite fdr its permanent establishment in the records of medical science ; but, as the maxim of the late illustrious and unfortunate Lavoisier, is deeply engraven upon my mind, I feel but little apprehension of being deluded from the proper track, by the fascinating incentives of hypothesis. ( 19 ) " We ought, in every instance, to submit our reasoning to *' the test of experiment, and never to search for truth, but by " the natural road of experiment and observation." Lavoisier. When assertions are made, either of a practical or theoretical nature, from a set of experiments, or a train of plausible rea- sbning, if, upon a close examination, they are found not to ac- cord with the experiments of others, well conducted, and more coincident with the ceconomy and operations of the animal body, it has long been a standing rule in medical philosophy, to con- sign them to merited oblivion. On physiological subjects, correct anatomy will always be re- garded as the polar star to successful researches ; and when she has performed her duty, the established laws of the animal body, like the compass which guides the ship at sea, ought on- ly to be entrusted with the important office of conducting us to the end of our journey. Mr. Abernethy says, " the removalof a quantity ofoxyge- " nous gas, from common air, is surely a curious circumstance; " if this be the effect of an action in the absorbing vessels, it " must much exalt our ideas of their subtility, and their apti- " tude or disposition to admit one species of matter, and to re- " ject another. That the absorption of one air, in preference " to another, depends upon this cause, I believe will not, upon " reflection, be doubted. It might indeed be suspected, that " oxygenous gas was separated from the atmosphere, by the " skin, as it is in the lungs, by chemical attraction: but it has " been proved, that carbonic acid is removed with equal celeri- " ty; and experiments on animal substances shew, in them, " a disposition rather to part with, than to imbibe, carbonic a- " cid. The removal of this air is, therefore, not likely to be " the effect of chemical affinity." My ( 20 ) My objections to this reasoning of Mr. Abernethy are, first, his data are far from being established ; on the contrary, the repetition of his chief experiments in my hands, fully disprove the existence of a gaseous function in the skin. The highly ingenious researches of Seguin, before mentioned, have given conclusions directly opposed to those of Mr. Abernethy; but they correspond with the result of my enquiries. In the second place, lymphatick absorbents cannot be satisfactorily demon- strated on the skin, though the best dissections have not been wanting, to ascertain their presence. The science of Physiolo- gy only embraces the healthy actions and powers of parts, the existence of which have been previously known to the anato- mist ; all beyond these prescribed limits must be uncertain, if hot entirely conjectural. But if oxygenous, carbonic and other gases are taken up by the skin, and carried into the system," why have they not been detected, cither in their gaseous form, or incorporated with the fluid circulating in the absorbing' vessels ? The next question that naturally occurs, is, how are these gases disposed of, admitting for a moment that they are actual- ly taken in by the lymphatick vessels of the skin ? As Mr." Abernethy has excluded chemical attraction from any agency in the case, they must be conducted through the course of the absorbents to the subclavian veins. The quantity of oxygen gas absorbed from the surface of the whole body, must be con- siderable, if the absorbents of the hand and wrist are capable of imbibing eight ounces in eight hours, as Mr. Abernethy asr serts ; would not then the blood in the left subclavian vein, which receives the thoracic duct, be of a more florid colour than that of the right, which only receives the lymphaticks of the right arm, and of the right side of the neck ? And lastly, if oxygen gas be absorbed by the skin, and conducted through the course of the lymphatick vessel* into the general circulation, may wc not call in question the ceconomy of the animal body ( 21 ) as the lungs appear fully competent to all the purposes of oxy- genating the system. A Chemist of this city, whose judgment I have reason to place great confidence in, informed me, that if gases were given out. by the skin, they might be discovered by holding the arm in a glass vessel filled and inverted in water. As I had ascertained the nature and proportions of the gases con- tained in the pump water at the Pennsylvania Hospital, where some of my experiments were made, no doubt was entertained but that some information might be derived from this mode of experimenting. Accordingly, a few experiments were made in this manner; as water, however, has been objected to, I will not relate them in particular, but deem it only necessary to: mention that the gases collected, differed in no considerable degree, from those which had been previously obtained from the water. As mercury has never been objected to, as a proper me- dium to experiment in, for accomplishing the objects of our present enquiry, a sufficient quantity was procured, and a tub arranged with necessary conveniences to contain it, as I was fully persuaded, that if any airs were thrown out by the skin, they could, under the circumstances of the following experi- ments, be easily detected. EXPERIMENT 1. Thermometer 73° A glass vessel being filled with, and inverted in quicksilver, all air that adhered to my hand and wrist was carefully sepa- rated by moving them in different directions, under the surface of the quicksilver for ten minutes ; they were then introduced into the inverted vessel and there retained for more than two hours ; for a few minutes, in the beginning of the experiment, my hand was in some degree benumbed with cold, but its usual warmth soon returned, and at the expiration of the time mentioned, little or no inconvenience was experienced, but ( 22 ) what arose from the pressure of the mercury. During all this time, not a bubble of either carbonic acid or azotic air, was seen to emanate from the skin. This experiment was made eight months ago, and has since been repeated in the presence of Professor Woodhouse, with precisely the same result. As lime water has always been regarded as a correct test for carbonic acid, it appeared plain, that if fixed air was thrown out by the skin, it would, while the hand and wrist were immersed in it, form, by chemical combination, carbonat of lime, and the milky color produced would afford a good criterion to judge of its emission. Under this impression the following experiment was made. EXPERIMENT 2. Thermometer 70° My hand and wrist were introduced into a jar containing lime water, whose purity was previously ascertained, and held in this situation for one hour ; during this time no carbonat of lime was formed, but on the contrary, the lime water, on with- drawing my hand, was as transparent as it was previously to its use. This experiment was repeated at another time, with no other variation than that of its being continued two hours, the result of which was the same as in the first; so that no decep- tion could have occurred in its performance. Mr. Abernethy, firmly believing that elastic gases were emitted by the skin, objected to water as a medium to experi- ment in, to discover this function, on account of its great dispo- sition to absorb carbonic acid ; all experiments, therefore, made in this manner, must be incomplete as relating to this acid gas, unless the state of the water be attended to, subsequent to their performance. With this consideration the following experiment was instituted. EXPERIMENT 3. Thermometer 58° Having half filled a convenient vessel with water, that had been previously boiled for some time, in order to separate all C 23 ) loose air that it mighfbe impregnated with; my foot and ankle were immersed in it, and retained in this situation for thuee hours, and then withdrawn. My object was now to ascertain, whether or not the water had imbibed carbonic acid ; to accom- plish which, a glass vessel was filled and inverted in the same water, a small handful of healthy leaves, of a species of gera- nium, were introduced into, the inverted vessel, and the whole exposed to the rays of the sun for four hours, during which time, no oxygen air was disengaged from the water. In this experiment, we may with safety conclude, that carbonic acid was not contained in the water, and consequently none Was emitted by the skin; for it has been proved to a certainty, that healthy leaves of plants will readily decompose carbonic acid, if contained in the water in which they are immersed, while in the light of the sun ; its coal will be devoured for food, and its oxygen escape in the form of pure air. Lest a few of those who may honor this dissertation with a perusal, should hesitate in admitting experiment 1, as satisfac- tory, on account of the pressure of the quicksilver, the follow- ing one was made, which proves, beyond a doubt, that carbon- ic acid gas is not emitted in the perspiration of animals. EXPERIMENT 4. Thermometer 56°. Having procured some pure hydrogen air, from diluted sul- phuric acid, and the filings of malleable iron, four ounce mea- sures of it, were thrown up into a glass vessel, previously filled and inverted in quicksilver : my hand and wrist, after all loose air was separated from their surface, as in experiment 1, were introduced into the inverted vessel, and kept in this situation, for three hours. My hand and wrist, being surrounded by,the hydrogen gas, in this experiment, suffered nothing from either the pressure or coldness of the quicksilver. Professor YVood- house observed this, as well as the chief experiments deUik-d in this essay ; and in his presence, the air in the vessel from which my hand and wrist had just been removed, was exar.an- ( 21 ) ed. Having ascertained that the volume of air had not been, in any degree, diminished, we passed up one ounce measure of it, over lime water, in an eudiometer; no milky appearance was observed by either of us : about three ounce measures of lime water were then passed up into the vessel containing the re- mainder of the air in which the experiment was conducted ; but no carbonic acid could be discerned, in either case. Dr. Rush relates, in his lectures, an experiment which in- duces him to believe in an scriform function of the skin : a light- ed candle, he says, in the morning, was extinguished by the air of the bed in which he had slept, the preceding evening. I do not hesitate to admit the experiment, as correct, but cannot subscribe to the inference of our ingenious Professor. The readiness with which respiration renders air impure, from the consumption of its oxygenous portion, is well known to every physiologist, and in my humble opinion, the contami- nation of the air in the bed, was owing to this process. This explanation will appear more probable, when we consider how often we lay, in the course of an evening's sleep, with our heads under the bed clothes. Having discovered, by all the above experiments, that the skin, with its membranes entire, has no connection with the of- fice of transpiring elastic fluids, I will next relate those experi- ments, which, in my own mind, undeniably prove, that gases are not absorbed from the external curface of the human body. EXPERIMENT 5. Thermometer 60° Five ounce measures of atmospheric air were thrown up into a glass vessel, previously filled and inverted in quicksilver; my hand and wrist, with the necessary precautions used in experi- ments 1, and 4, were introduced into it, and retained in this situation, with little or no inconvenience from the mercury, for three hours, and then withdrawn. We immediately exam- ( 25 ) ined the air in the vessel; its volume was not diminished, and, when passed through lime water, no milky color ensued ; which was an additional proof that the skin did not throw out,carbonic acid ; we next proceeded to ascertain whether or not any of the oxygenous portion of the air had been removed during the experiment ; for this purpose, one measure of it was passed up, over water, in an eudiometer charged with phosphorus, and in less than twenty four hours, the absorption of -££$ was com- plete. In this experiment, no addition or alteration occurred in the atmospheric air to which my hand and wrist had been exposed for three hours ; but with the view of giving complete satisfaction on the subject, the following experiment was per- formed. - EXPERIMENT 6. Thermometer 54° Five ounce measures of oxygen air, of 4 per cent purity, be- ing transmitted into an inverted vessel, previously filled with .quicksilver, my hand and wrist, freed from all adhering air under tie surface of the mercury, were introduced into it, and held in this situation three hours. Upon examination, the quantity of air had suffered no diminution ; it was then passed through lime water, and as turbidness did not occur, we infer- red that carbonic acid had not been given out by the skin ; the air was next tested, as in the former experiment, in the eu- diometer of Berthollet, and was found not in the least adulte- rated. The experiments ju*t related, prove, in the first place, that carbonic acid is not transpired; in the second place, that azotic air is neither emitted nor absorbed; and in the third place, that oxygen air is not inhaled by the skin of the human body. The care with which they were conducted, and the completeness of their plan, exclude all the deception which experimental enquiries, in the hands of inattentive observers, are often liaMe to. D ( 26 > In order to discover whether, or not, fixed air be removed from the external surface, by cutaneous obsorbents, the follow- ing experiment was made. EXPERIMENT 7. Thermometer 61° Five ounce measures of carbonic acid, obtained from carbo- nat of lime, by diluted sulphuric acid, were transmitted into a glass vessel, previously filled and inverted in quicksilver ; my hand and wrist were then introduced into it and kept in this situation for three hours. The volume of air was next attend- ed to, in order to accomplish the object of the experiment; it was found diminished in quantity only about half a drachm. The removal of which, I do not hesitate to ascribe to the combination of the carbonic acid with the perspirable fluid ; as my hand, when removed from the inverted vessel, was consi- derably moistened by this discharge. When we call to mind the affinity that naturally subsists between aqueous substances and this acid gas, the effect which we have mentioned is what ought to be expected ; besides, it is highly improbable that the skin, even if it were endowed with the power of absorption, would inhale carbonic acid which is thrown out by the lungs, as excrementitious, from the system, and refuse to absorb oxy- gen air, confessedly the pabulum vits, as was the case in expe- riments 5th and 6th. The experiments are now related, which have created, in my own mind, a firm belief, that a few physiologists, for whose talents in the science of medicine, I shall still cherish the high- est sentiments of respect, have, from the illusion of unforseen circumstances, which often render of no avail the best directed enquiries, erroneously imputed an ariform function to the skin. It is to Mr. Abernethy, whose pre-eminent abilities and in- dustry have long entitled him to the first rank in his profes- sion, that we are indebted for the best mode heretofore used in ( 27 ) the investigation of our subject. But while I am recording the merit which so justly belongs to this distinguished character, perhaps the zealous friends, and cultivators of Physiology will regret, that his ingenious researches had not terminated in the acquisition of truth. Their motives on this interesting'occa- sion would, I am conscious, have sufficient grounds of support; for one great source of ignorance and uncertainty in medicine is the accumulation of experiments and plausible theories, which are directly opposed to each other. In taking leave of this part of my essay, it will not be amiss to observe, that the preceding, as well as the following pages, are respectfully submitted to the examination of the public, not with the expectation of dislodging, immediately, opinions heretofore credited, but solely with the hope of calling the at- tention of others, who may ingenuously decide on the subject of the controversy ; as I shall be satisfied, either in being sup- ported or refuted, by such an interference. ( 28 ) EXPERIMENTS, AND • OBSERVATIONS ON THE IMPROPRIETY OF ASCRIBING ABSORPTION TO The External surface of the Human Body. PART SECOND. WHEN first the duty devolved on me to write an Inaugural dissertation, I intended to have confined myself to the consi- deration of those subjects which are above treated of ; but as time was not wanting, and the usual limits allotted to a publi- cation of this kind, were not exceeded, I resolved to extend my enquiries still further into the functions of the skin. Physicians, both in ancient and in modern times, have been at a loss to account for the manner in which many medicines produce their respective effects upon remote parts of the ani- mal body, when only applied to the external surface. Some have supposed that this phenomenon in medicine, could not be satisfactoiily explained, without admitting, that a portion of the articles were taken up by the absorbing vessels of the skin, and conveyed into the general circulation, to be directed to their appropriate parts, and there give rise to effects corresponding with the nature of the medicines employed. In behalf of this theory, we have on record the works of many respectable physicians, among which none are so emi- nently entitled to our consideration as the txperiments and ( 29 ) observations of Dr. Alexander Monro.* The doctor made a great variety of experiments on frogs, in different conditions, all of which tend to prove that, in them, opium, ardent spirits, and essential oils are absorbed from the external surface. He found that after the crural nerves of one frog were cut, and the hind half of the spinal marrow of two others completely de- stroyed ; camphor applied to the hind legs of all, produced the same effects, in nearly the same time, as when applied to a sound animal. " But to prove this absorption in fact," says our learned author, u I divided two frogs at the pelvis, two hours after the camphor had been applied to them in the above way ; I then pulled the skin off the fore part of their body ; and found, that the flesh and bowels had a smell of the cam- phor. To discover this more certainly, I cut them in pieces, and poured on one, rectified spirit of wine, and on the other, water ; and was sensible of the taste of the camphor, both in the spirit of wine, and in the water." As all the experiments made by the Edinburgh professor, were conducted without any regard to the lungs, which I shall soon prove to be an exten- sive apparatus of absorption, I do not hesitate to pronounce them incomplete, as the articles which he used might have passed into the system through this quarter, and not absorbed from the external surface, as he inferred. But even if I^was disposed to allow that his experiments completely prove that absorption does take place from the surfaces of frogs, they can- not, with any certainty be used in the investigation of our sub- ject. An amphibious animal is widely different, in its anato- mical structure, way of life and its oeconomy, from man. If then, it should hereafter be satisfactorily ascertained, by a se- ries of new experiments, or by a repetition of those of the pro- fessor, with a proper variation, that the frog is endowed with the function of cutaneous absorption, the discovery would not, in my mind, excite surprise, even if I should establish, by the ex- periments shortly to be detailed, that this office is unconnected with the oeconomy of the human body. * Physical Essays, vol. 3. ( 30 ) Dr. Barton, who perhaps is better acquainted with the func- tions of the lymphatick system, than any other man in Ameri- ca, is inclined to give some credit to cutaneous absorption in frogs. He informed me, in private conversation, that he had frequently observed, that if this animal was confined in a dry glass vessel, it became enfeebled, diminished in Its natural size, and scarcely able to leap; but if a small quantity of water was poured into the vessel, or the air in it only loaded with moisture, it soon acquired its wonted vigour, its body became plump, and its motions were usually lively. In the first part of the sixth volume of the Philosophical Transactions, an account is given of the Lacerta Subviolacea,* in which it is mentioned, that this animal was weighed at different times. On the 24th of March it weighed 342 grains, but in somewhat less than an hour, it weighed only 324 grains, having lost 18 grains. " It is a well assertained fact, however," says the ingenious naturalist, Dr. Barton, " that the weight of many of the Amphibia, particu- larly the frogs and lizards, is very various at different times, even in the course of the same day or hour. This difference of weight is often entirely independent on any aliment, whe- ther solid or fluid, being taken into the stomach, and must be ascribed to the absorption of water." Dr. Darwin, the ingenious author of the Zoonomia, says, *' that those who have remained half an hour in a warm bath, when they have previously been exhausted by exercise, or ab- stinence from food or fluids, have absorbed so much as to in- crease their weight considerably. Dr. Jurin found an increase of Weight to 18 ounces, by sleeping in a cool room, after a day's exercise and abstinence ; so much, in that situation, was absorbed from the atmosphere/'t * A species of Lizard first described by Dr. Barton, and railed by him Lacerta Subviolacea. t Zoonomia, page 440. ( 31 ) After having read the fair and conclusive experiments of Dr. Currie, the assertion of Dr. Darwin will appeal- highly error neous ; for in one instance, where death was caused by inanir tion, ne cutaneous absorption occurred, though the patient was imm*rsedin a warm bath for an hour. In J)r. Jurin's expe- riment, the absorption doubtless took place froni the lungs, and not from the external surface. , Jt is argued in favor of absorption, that animals live in hotj moist climates, without drink, and yet discharge a considerable quantity of humors, both by perspiration and urine ; and tha{ in some diseases of the human body, a much greater quantity of urine is discharged, than the quantity of drink taken in. That animals do live in hot, moist climates, without drink, we will readily admit, but that their thirst is allayed, their cutane- ous and urinary discharges carried on, in consequence of ab* sorption by the skin, is an induction which modern discoveries will not countenance ; for doubtless, in them, as in cases of hydropic and other diseases, where a much greater quantity of urine is often discharged than the quantity of drink taken in, the lungs supply the exigencies of the system. And what more particularly renders my reasoning at least plausible, on this subject, is the experience of a number of respectable physicians. Dr. Rollo* published an account of an interesting case of di- abetes, in which he mentions that the weight of the patient was not encreased by a continuance of ten minutes, in a bath of 110 degrees of heat. " In the year 1788, Dr. Currie happening to be at Buxton, made an experiment on the effects of bathing, on the weight of the body. After half an hour's immersion in the bath, he found his weight rather diminished than encreased. In the year 1790, he had a patient in diabetes, whose cuticle, as is usual in that disease, was in a morbid state. Being de- * Zoonomia, page 255. ( 32 ) sirous of trying how far the inordinate action of the kidneys might be affected by a gentle stimulus applied to the skin, he immersed him in a bath of the temperature of 96 degrees, weighing him before and after the immersion. In this case, no variation in the weight could be detected. Dr. Currie after- wards made five different experiments of the same kind, upon himself, varying the heat of the bath, from 87 to 95 degrees; but he could never, in any one instance, find his weight aug- mented. It may however be said, that though in diabetes, where the epidermis is diseased, no liquid is inhaled ; and tho' in health, when the vessels are full, no absorption may take place ; yet, when the body is wasted, from a want of proper food through the stomach, the plastic powers of nature may be employed to supply the defect, and to excite an inhalation through those pores on the surface, by which an exhalation is usually performed. To prove that this does not happen, Dr. Currie relates, very minutely, a remarkable case of dysphagia, where death was the consequence of inanition, notwithstanding every attempt to support the system, both by the rectum, and by the surface. This patient, on different occasions, stepped perfectly naked, upon Merlin's balance, immediately before im- mersion ; and again immediately after it, his body being pre- viously dried. The weights were never moved. The result was surprising ; for Dr. Currie could not distinguish the slight- est variation in the weight of the body, though the beam would have detected a single drachm, though the immersion had been continued for an hour, and though a constant friction had been kept up, nearly the whole time, on the inner surface of the thighs, with the view of encreasing the action of the absorbents. If the non-absorption by the surface of the body be established, it will, Dr. Currie observes, ascertain, that, in the ordinary course of things, contagion is received into the system, by the lungs only, and will, he thinks, justify a practice, which he has been informed, is common among our more experienced seamen, on the coast of Guinea, and other warm climates, who when exposed, during the night, to a breeze from the marshes ( 33 '. ) wrap their heads in a sea-cloak, or other covering, and sleep fearless oh the deck, with the rest of their bodies nearly ex- posed." ■■.'■* Since the celebrated French Philosopher, Bichat, suggested that absorption took place from the lungs, and published the experiments corroborative of his opinion, we have not been at a loss to account for the manner in which certain volatile articles applied to the skin, have,-in a short time, passed into the system, and manifested their presence by tlte effects which they produce on the excretions of the body. The following quotation from this auttior, will afford the reader an epitome of his theory. Extract from a work entitled " Recherckes Phijsiologiques sitr fa Fie e& la Mort :