ON THE SPECIAL FUNCTION OF THE SKIN
BMJ (Clinical Research Edition)
THEzE is perhaps no function in the living body which owes less to the labours of the physiologist, than that of the extensive and highly organised structure designated the skin. The antomy of the common integument is probably exhausted; its rational physiotogy has still almost to be begun. Yet that the proper action of the skin is most intimately connected with health, is universally admitted; and there are not wanting many isolated facts and experments which go to prove that it is little less
... t it is little less immediately necessary to general vital manifestation than the function of the lungs. Still, we are in signal ignorance of the nature of the act in the economy which the skin performs; and the best ntellects in our profession have hitherto shrunk from the task of explaining in what way the elimination of a considerable quantity of water, holding in solution infinitesimal proportions of common salts and gases, is indispensable to health and life. One of the last and best authorities in physiology (Joannes Miller) avows that "the object of the cutaneous exhalation is not elucidated by its analysis"; and more impressively still, the great Derzelius declares, "That the elimination of the small quantity of solid matter which the sweat contains cannot be the end of the function of the skin." He continues: " The perspiration has been said to regulate or depress the temperature of the body when raised by violent exercise, or any excessive heat of the surrounding air. But the itimate conuexion that exists between the function of the skin and the bodily health, proclaims it to have been instituted for yet another purpose, the nature of which is unknown to us." It is now more than ten years since I -attempted a solution of this physiological problem; and as aRl my subsequent inquiries have only confirmed me in the conclusions at which I then arrived, I gladly avail myself of the opprtunity afforded by the Physiological Section of the Medical Society of London to revive a subject which I -cannot help regarding as both interesting and important, -and now present it for the thoughtful consideration of the present meeting. Water, it is well k-nown, is the principal constituent of -the cutaneous exhalation; sweat is composed of from 98j to 99j parts of pure water, and from If to a poor A per cent. of solid ingredients, these consisting in principal part of common salt and epithelial scales. Nature, so truly economical in all her processes, we may be well assured, would not waste 99 in 100 parts of even so cheap a fluid as simple water to wash away a solitary unit of inoffensive matter; and we accordingly find physiologists in the later years of the last century, under the influence of the brilliant discovery and admirable industry of the immortal Black, arriving at what has almost up to the present hour been held a satisfactory solution of the fact, that there -occurred an extraordinary elimination of simple water by the skin. The end and object of the cutaneous exhalation, it was said, was, by means of evaporation from the general surface, to regulate the temperature of the animal body. Now, it is quite certain, that this idea has been taken up in far too wide an acceptation; and that later, more carefully conducted experiments on animal heat do not bear out the authors of the earlier series in the conclusions to which they came. The conclusion sanctioned by the expeninents of Fordyce, Blagden, Solander, and Banks, is that a human being or an animal may remain for almost any length of time in an atmosphere raised to twice the heat of te body, without injury to health, and without the acquisiton of a single degree of temperature. But our countryman, Dr. Crawford, and the Messrs. Dela--d Bger, of Pis, whoe epe ets have some-times been quoted as supporting the abrd on i, are, without a single exception, directly opposed to them. In their experiments in the heated chamber, the Fech physiologists found that the health of the animal which were their subjects was speedily and very seiously affected; that few of them withstood exposure to.its atmosphere for an hour without beini reduced to extremity; and that, when taken out either m a dying state% z at the moment of their death far from having retaine !heir normal temperature, they had a temperature from I lko to 15ij F. higher than it had been on their entrance. Nor was the case different when man was the subject of experiment, and inferior degrees of temperature were tried. M. Delaroche's internal temperature on entering the heated chamber on one occasion was found to be 29J' R.; on quitting it, after a stay of no mose than eight minutes, his internal temperature indicated as many as 3340 R.; so that in this very short space of time, the temperature of the internal parts of M. Delaroche's body had actually gained 40 Reaumur, equal to 90 of Fahrenheit's scale. These experiments then prove that the commonly received opinion of the great power possessed by the animal body, in virtue of evaporation from the general surface, of maintaining its standard temperature in the midst of an atmosphere by many degrees higher than its own, is unfounded. Nor is the case different when the effects of exposure to much lower temperatures than those employed by the French physiologists are made the subject of inquiry. In his voyage from EAngland to Ceylon, Dr. John Davy found that the temperature of his companions rose gradually as warmer latitudes were gained; and, on arrival at their destination, that it was from 2-7°F. to 3.60 F. higher than it had been on leaving the shores of Great Britain. More than this, the temperature of the lower animals at all events (and I believe it is not otherwise with man), is influenced by the seasons of the year. The excellent observer I have just quoted, found the temperature of the sheep to be from 1" to 20, and even 3°F . higher in summer than in winter. And Dr. Edwards ascertained that whilst in the month of Febmary the mean temperature of a number of house-sparrows was 1050 F., in April it was 1080 F., and in July as high as 1110 F.; a difference of six degrees Fahrenheit between the coldest and the hottest months of the year. It is much to be regretted that there are no corresponding observations on the temperature of the human subject. But we have now such confidence in the uniformity of the physical laws which influence the organic world, that it can be predicated with certainty that the temperature of the body of man also rises and falls with the rise and fall in the temperature of the seasons. Man, like everything else, is fashioned in harmony with the varying circumstances that surround him as the denizen of every region of the earth; and if he have the wonderful attribute of preserving his temperature nearly at the same degree under the equator and at the pole, we can now say assuredly that he does so in virtue of something very different from the greater or less activity of the exhaling function of his skin. The evolution of heat in the animal hody is not, in fact, accomplished otherwise than it is iD our stoves and furnaces-it is the consequence of the direct combination between the air of the atmosphere and the hydrocarbonaceous or carbonaceous matters, which in the one case constitute the food, in the other the fuel; and just as the heat of a furnace is great in the ratio of the strength and continuity of the blast, so is the temperature of an animal inseparably connected with the energy of its respiration. Unprotected by clothing, at rest, and feeding upon roots and fruit and grain, the power of the human body to maintain a temperature of 980 F. appears to be in relation with an air temperature of from 800 to 900 F.; in temperate regions, in a state of repose, and living on a mixed diet of animal and vegetable substances, we must still be well clothed if we would feel comfortable under any temperature of the atmosphere short of 640 or 650 F. In the frgid zone, again, we must be shroudd in felt and fur, Ad be extraordiily on 30 April 2019 by guest. Protected by copyright.