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Mr. Milnes avails himself of the opportunity to promote the pacific intentions of his friends M. Guizot and Sir Robert Peel:
. For honest men of every blood and creed
Art. IV.- Animal Chemistry; or the Application of Organic
Chemistry to the Elucidation of Physiology and Pathology. By Justus Liebig, M.D. Edited from the German MS. by William Gregory, M.D., Professor of Chemistry, King's Col
lege, Aberdeen. 8vo. London, 1842. THE recent progress of Chemistry, especially of Organic
Chemistry, has been rapid and most interesting. Throughout Europe several distinguished men have for a good many years been assiduously devoted to its cultivation; and we are now beginning to reap the benefit of their exertions. In a late article we had to notice the masterly work of Professor Liebig on · Agricultural Chemistry;' and already we have, from the same pen, a no less remarkable volume on · Animal Chemistry.'
As his new theme, in one point of view, concerns us all even more nearly than that of agriculture, we shall endeavour to give our readers some notion of the kind and degree of light which our author's labours promise to throw on the obscure and difficult, but most important subject of physiology.
The readers of the · Agricultural Chemistry' will remember that he has there developed, and, as we think, established by a very beautiful inductive argument, his theory of fermentation, putrefaction, and decay; or, to speak more generally, of chemical transformation or metamorphosis. In order to the understanding of the present work, it is desirable that we should state, very briefly, the nature of that theory, on which so many of its details are founded.
Professor Liebig, then, applies the name of metamorphosis to those chemical actions in which a given compound, by the presence of a peculiar substance, is made to resolve itself into two or more new compounds : as, for example, when sugar, by the presence of ferment or yest, is made to yield alcohol and carbonic acid.
There are various forms of metamorphosis. Sometimes the elements of the ferment, or exciting body, do not enter into the composition of the new compounds : such is the case in the fermentation of
At other times all the bodies present contribute to the formation of the new products. Thirdly, in one form of metamorphosis, namely, that of decay, or eremacausis, the oxygen of the air is essential to the change: as when alcohol is converted into acetic acid, or wine into vinegar. When an inodorous gas is one of the products, the process is called fermentation; when any of the products are fetid, it is called putrefaction : but these distinctions are not essential; for putrefying animal matters will cause sugar to ferment, as well as common yest. The fetid smell of putrefaction is chiefly owing to ammonia; and hence it is observed noi only in the fermentation of animal matter, but also of such vegetable bodies as contain nitrogen, and therefore yield ammonia.
Now the explanation given by our author of these and similar changes is this: that the ferment, or exciting body, is invariably a substance in an active state of decomposition. Its particles are therefore in a state of motion; and this motion, being communicated to those of the body to be metamorphosed, is sufficient to overturn their very unstable equilibrium, and to cause the formation of new and more stable compounds. The more complex the original compound, the more easily does it undergo metamorphosis. The Professor has produced, in support of this doctrine, an extraordinary number of facts, and has, by strict induction from these, demonstrated it almost mathematically.
It appears to us that he has for ever banished the notion of the catalytic force-an unknown and mysterious power which some writers had invoked to explain the phenomena of chemical transformations.
When we turn our attention to the living animal body, there are certain processes or operations which at once present themselves as the most interesting. Among these may be mentioned respiration, nutrition, the waste and supply of matter, digestion, secretion, and excretion, with the bearings of all on health and disease. On all of these subjects the views of the author are equally original and interesting.
• Wonders,' he remarks,“ surround us on every side. The formation of a crystal, of an octahedron, is not less incomprehensible than the production of a leaf or of a muscular fibre; and the production of vermilion from mercury
and sulphur is as much an enigma as the formation of an eye
from the substance of the blood.'--p. 12. There are two essential conditions of animal life. First, the assimilation or appropriation of nourishment; secondly, the continual absorption of oxygen from the atmosphere. Now the quantity both of food and of oxygen introduced into the system of an adult is very considerable, and yet the weight of his body does not increase : it is clear, therefore, that as much must be given out as is taken in. But in what form is the oxygen, for example, given out? It is invariably in combination with carbon or hydrogen, or both, as water and carbonic acid gas. The carbon and hydrogen are derived, ultimately, from the food. By comparing the amount of oxygen absorbed with that of carbonic acid given out, and with that of the food consumed, the author demonstrates that, •The amount of nourishment required for its support by the animal body must be in a direct ratio to the quantity of oxygen taken into the system. But the amount of oxygen inspired varies very much. It is increased by motion or exercise, which increases the number of respirations : it is increased by cold, which renders the air more dense; and it is also increased in proportion as the barometer rises, for the same reason.
• The consumption of oxygeu in equal times may be expressed by the number of respirations : it is clear that, in the same individual, the quantity of nourishment required must vary with the force and number of the respirations. A child, in whom the organs of respiration are naturally in a state of great activity, requires food oftener, and in greater proportion to its bulk, than an adult, and bears hunger less easily. bird, deprived of food, dies on the third day; while a serpent, which, if kept uuder a bell-jar, hardly consumes in an hour so much oxygen as
that we can detect the carbonic acid produced, can live without food three months and longer.
'In summer and winter, at the pole and at the equator, we respire an equal volume of air.-In summer, the air contains aqueous vapour, while in winter it is dry. The space occupied by vapour in warm air is filled up by air itself in winter: that is, an equal volume of air contains more oxygen in winter than in summer.
• The cold air is warmed in the air-passages and in the cells of the lungs, and acquires the temperature of the body. To introduce the same volume of oxygen into the lungs, a smaller expenditure of force is necessary in winter than in summer; and for the same expenditure of force, more oxygen is inspired in winter than in suminer.
* The oxygen taken into the system is given out again in the same forms, whether in summer or in winter: hence we expire more carbon in cold weather, and when the barometer is high, than we do in warm weather; and we must consume more or less carbon in our food in the same proportion : in Sweden more than in Sicily; and in our more temperate climate a full eighth more in winter than in summer. Even when we consume equal weights of food in cold and warm countries, infinite wisdom has so arranged, that the articles of food in different climates are most unequal in the proportion of carbon they contain. The fruits on which the natives of the south prefer to feed do not in the fresh state contain more than 12 per cent. of carbon, while the bacon and train oil used by the inhabitants of the Arctic regions contain from 66 to 80 per cent. of carbon. It is no difficult matter, in warm climates, to study moderation in eating, and men can bear hunger for a long time under the equator; but cold and hunger united very soon exhaust the body.
• The mutual action between the elements of the food and the oxygen conveyed by the circulation of the blood to every part of the body is the SOURCE OF ANIMAL HEAT.'—p. 17.
We are tempted to continue our extracts from this part of the work. Speaking of the uniform temperature of the animal body, and of the effects of cooling, he says:
* The most trustworthy observations prove that in all climates, in the temperate zones as well as at the equator or the poles, the temperature of the body in man, and in what are commonly called warm-blooded animals, is invariably the same; yet how different are the circumstances under which they live ?
*The animal body is a heated mass, which bears the same relation to surrounding objects as any other heated mass. It receives heat when the surrounding objects are hotter, it loses heat when they are colder, than itself. We know that the rapidity of cooling increases with the difference between the temperature of the heated body and that of the surrounding medium; that is, the colder the surrounding medium the shorter the time required for the cooling of the heated body. How unequal, then, must be the loss of heat in a man at Palermo, where the external temperature is nearly equal to that of the body, and in the
polar polar regions, where the external temperature is from 70° to 90° lower. Yet, notwithstanding this extremely unequal loss of heat, experience has shown that the blood of the inhabitant of the Arctic circle has a temperature as high as that of the native of the south, who lives in so different a medium. This fact, when its true significance is perceived, proves that the heat given off to the surrounding medium is restored within the body with great rapidity. This compensation takes place more rapidly in winter than in summer, at the pole than at the equator.
' In the animal body the food is the fuel ; with a proper supply of oxygen we obtain the heat given out during its oxidation or combustion. In winter, when we take exercise in a cold atmosphere, and when, consequently, the amount of inspired oxygen increases, the necessity for food containing carbon and hydrogen increases in the same ratio; and by gratifying the appetite thus excited, we obtain the most efficient protection against the most piercing cold. A starving man is soon frozen to death; and every one knows that the animals of prey in the Arctic regions far exceed in veracity those of the torrid zone. Our clothing is merely an equivalent for a certain amount of food. The more warmly we are clothed the less urgent becomes the appetite for food, because the loss of heat by cooling, and consequently the amount of heat to be supplied by the food, is diminished. If we were to go naked, like certain savage tribes, or if in hunting or fishing we were exposed to the same degree of cold as the Samoyedes, we should be able with ease to consume 10 lbs. of flesh, and perhaps a dozen of tallow candles into the bargain, daily, as warmly-clad travellers have related with astonishment of these people. We should then, also, be able to take the same quantity of brandy or train oil without bad effects, because the carbon and hydrogen of these substances would only suffice to keep up the equilibrium between the external temperature and that of our bodies.
The Englishman in Jamaica sees with regret the disappearance of his appetite, previously a source of frequently recurring enjoyment; and he succeeds, by the use of Cayenne pepper and the most powerful stimulants, in enabling himself to swallow as much food as he was accustomed to take at home. But the whole of the carbon thus introduced into the system is not consumed: the temperature of the air is too high, and the oppressive heat does not allow him to increase the number of respirations by active exercise, and thus to proportion the waste to the amount of food taken. Disease of some kind therefore ensues.
On the other hand, England sends her sick, whose diseased digestive organs have in a greater or less degree lost the power of bringing the food into that state in which it is best adapted for oxidation—and therefore furnish less resistance to the oxidising agency of the atmosphere than is required in their native climate-to southern regions, where the amount of inspired oxygen is diminished in so great a proportion; and the result, an improvement in the health, is obvious. The dişea sed organs of digestion have sufficient power to place the diminished amount of food in equilibrium with the inspired oxygen : in the colder climate, the organs of respiration themselves would have been consumed in furnishing the necessary resistance to the action of the atmospheric oxygen.