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CHAPTER VIII.
HIS ESSAY ON THE SKIN AND LUNGS.

    "It is madness and a contradiction to expect that things which were never yet performed should be effected, except by means hitherto untried."—Bacon, Nov. Org. Aph. 6.

When we consider the object which the distinguished Author had in view, in the immortal Work whence we have taken the foregoing simple but instructive aphorism, we cannot but perceive how highly suggestive it is to those engaged in scientific researches, or how necessary to be borne in mind by those who are really aware of the present state of Medicine and Surgery, and desirous of seeing them become a definite science. Nor does it appear inappropriate to the consideration of Abernethy\'s experimental inquiries into the functions of the skin and lungs. An extended investigation—of which his paper on these subjects contains an excellent type, and is in part a practical application—would be a great step towards the creation of a real science, and would certainly fall within the "means untried" of Lord Bacon.

Although the latter part of the last century, and the first half of the present, have been very remarkable for the number of distinguished men who have flourished during that period, in almost every branch of knowledge; yet neither the bar nor the senate, neither literature nor any of the sciences, can boast of greater men, nor lay claim to more positive improvement, than Chemistry.

If we only consider that interval between the discovery of oxygen by Priestley, in 1774, and the conclusion of Sir Humphrey Davy\'s labours, Chemistry almost seems like a new science; and it continues to advance with such rapidity, and is daily opening62 out so many new questions, that the most accomplished chemist of one year is never sure how much he may have to learn the next; nor, unless he reasons with great caution, how much he may have to unlearn.

To a physiologist, who requires assistance from all branches of science, Chemistry must always be an interesting study. When we lay aside all speculations as to what is the abstract nature of Life, and study that which is the proper object of philosophy—that to which it seems the faculties of man are limited—namely, the laws in obedience to which the phenomena in nature occur; and apply the knowledge thus obtained to the occurrences which take place in the human body; we soon discover that, whatever the abstraction "Life" may be, we live proximately, in virtue of certain changes in various forms of matter; as food, air, the various constituents of our bodies, &c.; and that these consist of multiplied separations and rearrangements of their respective elements, which it is the special province of Chemistry to examine.

If we investigate the changes of the living, or the structure of the dead, with these objects,—we shall be in no danger of perverting Chemistry to purposes to which it is inapplicable. When, however, we proceed a step further, and seek to give a chemical expression to various uses and relations of different parts of the body, the greatest caution is required.

In the first place, in a machinery which is a practical application of a great many sciences, it is to the last degree improbable that they can be expressed by any one.

Again, to estimate the true meaning—the physiological interpretation of many changes which might be in their proximate sense chemical,—a greater familiarity with the phenomena of disease is necessary than usually falls within the inquiries of the most scientific chemist.

To a person acquainted only with the ordinary phenomena of health, or who is not even something also of a philosophical pathologist, Chemistry is for ever suggesting tempting analogies, which are constantly tending to mislead him to conclusions on insufficient data; and to examine and rest too much on the chemical facts deducible from one or other function, without sufficiently63 attending to the physiological relations of that function with all others.

In fact, for want of due caution, or it may be of a sufficient range of information, the assistance which Chemistry has hitherto rendered to Physiology has been attended with so many assumptions, that it is extremely difficult to say on which side the balance lies—of advantage or error. We are aware that at this moment there is a contrary feeling—a kind of furore for chemical solutions of physiological phenomena. We believe the caution we venture on suggesting was never more necessary.

The discovery of oxygen gas by Priestley, not only gave a great impetus to chemical inquiries, but affected Physiology in a very remarkable manner; when it was found that the more obvious phenomena of all cases of ordinary burning—lamps, candles, and fires of every kind—consisted mainly of the chemical union of charcoal and oxygen (carbonic acid); and again, when it was discovered that animals, in breathing, somehow or other produced a similar change, one may conceive how ready every one was to cry, "I have found it. The heat of animals is nothing more than combustion! We inhale oxygen; we breathe out carbonic acid; the thing is plain. This is the cause of animal heat!"

It has always struck us as a curious thing that chemists should have attached such a dominant influence, in the production of heat in animals, to the union of carbon and oxygen; because nobody is necessarily so familiar as they are with the fact that the evolution of heat is not at all peculiar to the union of these bodies, but is a circumstance common to all changes of every kind, in all forms of matter—there always being either the absorption or the evolution of heat.

There is no doubt that the analogy is very striking between the changes which appear to be wrought in respiration, and those which take place in ordinary combustion. A very little consideration, however, shows that the idea that respiration is the cause of animal heat, or that it is due to any other change of oxygen merely, is not only an assumption, but in the highest degree doubtful. In the first place, the carbonic acid thrown out when we expire, is certainly not made by the immediate union of the64 oxygen inspired with the charcoal expired; secondly, nothing is so obvious that in respiration there is an immense quantity of heat thrown out of the body. But as it is very desirable that the subject of this paper of Abernethy\'s on the Skin and Lungs should be understood, we will give the reader a simple view of the nature of these important organs; and as one (functionally considered) is as much a breathing organ as the other, we will say a few words first of the lungs.

In all animals19, the blood, or other fluid in which the elements of nutrition are sent to all parts, is exposed to the action of the air; and this is what we call breathing or respiration; and the exposing of the blood to air is so arranged that both fluids are in more or less rapid motion. The staple constituents of the air, so to speak, are about one-fifth oxygen and four-fifths nitrogen gases, with about two parts perhaps in a thousand of carbonic acid; and although, as we too well know, the air is occasionally polluted by many additions, yet, whether we take air from the top of Mont Blanc, or a cellar in London, the staple principles of oxygen and nitrogen have their proportions unchanged. The air breathed by animals who live in the water is somewhat differently constituted; the proportion of oxygen is considerably greater, probably about as much as one-third or thirty-two parts in one hundred; so that fish breathe a more highly oxygenated air than we do.

Now it is found that, when we inhale the air of the atmosphere (that is to say, one-fifth oxygen and four-fifths nitrogen), we expire some oxygen, some carbonic acid, and some nitrogen also; and to ascertain the actual changes which took place, was the object of Abernethy\'s inquiry.

The subject is one of great interest to the public; and, in justice to Abernethy, we should remark (that which perhaps a few more years may render it more important to record), that this essay was written more than half a century ago—1793.

65

Thousands die every year of affections of the lungs; and many diseases of these organs, if not in their nature incurable, have too generally in practice proved to be so. There are not wanting, however, many persons who ascribe these mournful results, not so much to the abstract difficulty of the case, as to imperfect and erroneous views of the functions and relations of these important organs; and who entertain the opinion that the investigation of the subject has been, either from preconceived notions, from a too limited view of the phenomena, or from some other cause, so infelicitously conducted, that the conclusions arrived at have been either merely assumptions, extremely doubtful, or absolutely erroneous.

It is sufficiently obvious that if we are ignorant of the use of any part of a machine, it must be the most unlikely thing in the world that we should know how to set about repairing it when it is out of order; and the matter must be still worse, if we should happen to ascribe to certain parts of it purposes different or contrary to that which they as really fulfil. So, in an animal, if we are ignorant of the use and relations of any organ, it is very improbable that we can understand the nature of its disorders, or treat them in any case successfully, except by the merest accident, which, though it may waken us up to a sense of our ignorance, leaves us so blind to the causes of our success that we have no power of repeating it.

Now this is pretty much the actual state of affairs in respect to diseases of the lungs. No investigation of any organ is worth anything, unless it include its relations with other organs in the same machine.

What should we ever learn by looking at the mainspring of a watch, apart from the general machinery to which it belongs? Though we should look for ever, and employ a microscope to boot, it is clear we should never arrive at the perception of its true relations.

Abernethy\'s inquiry derived great interest from the investigation of the skin by which it was preceded, and which seems to have formed his primary object. A few words on this wonderful organ may help the unprofessional reader to form some estimate66 of its relations and importance. As, in all animals, it is the surface in immediate contact with external influences—the first which attracts our notice—the first which we instinctively interrogate as to the state of the animal, so it is of all others the first which presents to us the evidence of design and adaptation. We tell the climate an animal inhabits, with moderate certainty, by looking at the skin; and if we occasionally meet with apparent exceptions, further examination usually shows that they exemplify the more strikingly the unity of plan. Thus we may find animals who inhabit hot regions furnished with a somewhat warm covering of the skin; as the tiger, for example: but when we examine the eye, and inquire into the habits of the animal, we find that he preys or feeds at night, when the atmosphere is charged with damp and cold.

We know that the animals whence we obtain our furs inhabit cold regions. The changes in the same animal are not less instructive. Animals placed in certain circumstances, in which they require greater warmth, have increase of covering, and vice versa. Again, the tendency to become white, in those inhabiting cold regions, is a very interesting adaptation, although I am not aware that it has been satisfactorily explained. Two things, however, are certain: that they are placed in different circumstances as regards the relation to heat, and would reflect a great quantity of light, which, in its intensity in snowy regions, might be prejudicial, as there is no doubt of the influence of this principle in animals. Again, it is a very common arrangement that animals should take the colour of the ground they occupy; and this is sometimes very curiously exemplified. I have observed in the common hunting-spiders which inhabit some palings in a garden in the country, that they are of different shades, but they all more or less resemble that part of the old paling on which they are found. Those which we see on the ground are generally of some dark colour. Birds exemplify in a very remarkable manner the adaptation of their external coverings to the requisitions which their habits establish. All animals may be said to be surrounded by an atmosphere of their own, and they are not therefore, strictly speaking, in contact with the atmosphere; but67 when they are exposed to air in motion, this stratum is blown aside, and the atmosphere is brought in contact with the surface. Its refrigerating influence is now felt; and, just as a boy cools his broth by blowing on it, a fresh stratum of cold air is constantly brought to the surface.

The power of resisting or limiting this refrigerating influence is somewhat differently conferred in different animals: in the healthy human subject, by increased activity of the vessels of the skin, which induces greater heat. Birds, in their rapid flight, and especially in the more elevated regions of the atmosphere, are exposed to intensely refrigerating influences. These are met by the surface being clothed first by fine feathers, the worst of all conductors of heat, and these are overlapped, where they meet the atmosphere, in such a way that the bad-conducting property of the feathers is increased by the mechanical arrangement of them. Again, the respiration of birds, which (as we contend) is a refrigerating process, is very restricted; although, for want of due consideration of all the circumstances, and especially of certain analogies afforded by insects, very opposite views have been entertained. Domestic animals (birds inclusive) impressively suggest the refined adaptation of colour even, of the whole surface, to the altered position of the individual. Nothing is more striking than the general uniformity of colour in wild animals—few things more familiar than their infinitely varied hues when domesticated. Now it is certain that these differences have a meaning, and that their relations are important; but when we extend these thoughts from the coverings of animals to the consideration of surface, whether of animals or vegetables, what wonderful things occur to us. Every variety of colouring which we observe in domestic animals, every spot on an insect\'s wing, every pencilling on a a flower, places the individual in a different relation, so far, to light, heat, and other powerful agents in nature.

Or if we look from another point of view—we cannot walk by a hedge-row in summer without observing how very small the differences of light and aspect are, which seem on the same soil to confer on the same species of flowers such numerous varieties68 of colour. I have most frequently observed this in the common cranes-bill, or wild geranium.

In order to estimate correctly the value of these surfaces to the animal or vegetable, it is obviously of great importance to us to know what they do; and if they give off any thing, to ascertain its nature. That either animal or vegetable may be healthy, the processes of nature, whatever they are, must be carried on; and we may be assured, that the fragrance of the rose is just as necessary an exhalation from the plant, as it is an agreeable impression to us.

But all animals may be said to breathe quite as much by their skin as by their lungs. Leaves, too, are the breathing surfaces of vegetables; and, therefore, to ascertain the facts in the one, without inquiring into those observable in the other, would be likely to fog our reasoning and falsify our conclusions. The first impression we obtain from all animals is from external form and appearance—from, in fact, its outward covering. It was the first organ to which Abernethy devoted his most particular attention; and here again his investigations show how little those knew of his mind who imagined that his thoughts were restricted to any one set of organs.

In whatever light we view it, the skin is, in all animals, a most important organ; and so much so, as—drolly enough—with the exception of the human subject, to have been long popularly so considered. Yet so imperfect have been the investigation of its functions, that we are at this moment chiefly indebted to the early experiments of Abernethy for what we know that is positive on the subject. The original experiments of Sanctorius were quantitative and, as general truths, of sufficient importance to have excited more attention. Cruikshank\'s were highly acceptable; but they were less numerous and less varied than those of Abernethy; whilst the labours of Edwards, though exhibiting great industry and zeal, were by no means so conclusive as those of Abernethy. Edwards\' experiments served to strengthen and confirm, by the analogy afforded by other animals, conclusions drawn by Abernethy from the more secure premises furnished by the observation of corresponding functions in man.

69

Mr. Abernethy\'s inquiry was first directed to ascertain what the skin actually gave off from the body; and secondly, what changes took place in the air which we draw into the lungs (inspiration). We will endeavour to give some idea of these experiments. They were very simple—they involved no cruelty, like those of Edwards—and they were many of them such as the public might repeat without difficulty.

Very useful would it be, if persons who have leisure would sometimes engage in physiological inquiries. They would find them to be extremely interesting; and a series of facts would be easily collected, from which the physiologist might obtain the most valuable information, but which, engaged as most of us are in applying physiology to the correction of disordered functions, we can seldom collect for ourselves, ex............
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