animal obtains in its food the very same princi-, for the process of respiration. Fat conples on the presence of which the nutrition of tains much more carbon, with an excess of the carnivora entirely depends.'-pp. 45–48. hydrogen, but serves the same purpose. The chief difference between the carnivora and herbivora would seem to be The author goes on to show that vegetables alone can produce proteine, which, this :-in the former, the carbon consumed as it is the most complex product of vege-in respiration must be derived from the table life, is the starting-point of the still more complex animal products-from the food, which being identical with their boblood, the origin of all the solids, to the dies, we may say that the carbon is suplast and most important product of animal plied by the daily waste of their tissues, life, namely, the substance of the brain food. But, to furnish enough of carbon to life, namely, the substance of the brain this waste being compensated by their and nerves. Thus we perceive that the food of herbivorous animals contains the keep up the heat of the body in this way, very same principles (compounds of pro-accelerated by motion. Hence the restthe waste must be prodigious: it must be teine) which constitute the food of carniless habits of carnivorous animals; hence vorous animals. They are mixed, however, in the former case, with a large pro-hunting alone must eat five times as much the reason why the savage who lives by portion of substances containing no nitrogen-such as sugar, starch, gum, &c., the uses of which will shortly appear. flesh as if he lived on a mixed diet; hence the total absence of fat in his body, as well as in that of all carnivorous animals. In The food of vegetables is invariably inthe herbivora the waste of matter is far less organic matter, carbonic acid, ammonia, water, and salts. The results of vegeta-latively rapid, and is fully compensated by the retion are, compounds of proteine, starch, latively small amount of proteine in their sugar. gum, &c., and finally. fat or oil: all food: they eat incessantly; the great mass of of which serve to support life in animals their food, (starch, &c.) is consumed in resthe compounds of proteine for nutrition; the other matters, as we shall see, for respiration. The food of animals is always organised matter. Plants form or produce proteine, which in some form is essential to animals, as the latter cannot form proteine from substances that do not contain it. Proteine being once given, the animal organism forms from it all its peculiar tissues, which are never found in vegetables. Thus, no vegetable can produce nervous matter. piration; thus rendering needless a rapid change of matter in the animal tissues. The whole of these admirable arrangefully in the present work; and nothing ments are brought out clearly and beautican be more satisfactory than the author's array of established facts, with the argu ment founded on them. The young animal receives the constituents of its blood in the caseine of the milk. A metamorphosis of existing organs goes on, for bile and urine are secreted: the matter of the metaurine, of carbonic acid, and of water; but the morphosed parts is given off in the form of butter and sugar of milk also disappear-they cannot be detected in the fæces. It is to the author that we owe the discovery that vegetables, especially the leguminous seeds, produce vegetable caseine, a substance absolutely the same with the "The butter and sugar of milk are given out peculiar principle of milk, inasmuch that, in the form of carbonic acid and water, and when curdled, it is not to be distinguished the clearest proof that far more oxygen is abtheir conversion into oxidized products furnishes from skimmed milk cheese, either chemi-sorbed than is required to convert the carbon cally or physically. Thus the vegetable and hydrogen of the metamorphosed tissues world produces white of egg, fibrine, and into carbonic acid and water. milk; these are all convertible into blood, from which any of them may be again produced where it is required. They are all compounds of proteine, as above stated. What, then, is the use of the sugar, starch, &c., in the food of the herbivora ? or what is the use of the sugar of milk, and fat (butter), in the food of the young carnivora ? This important question is treated in the most profound and ingenious manner; and the author demonstrates that these substances-which may all, except fat, be considered as compounds of carbon and water (Prout)-serve to furnish carbon The change and metamorphosis of organized tissues going on in the vital process in the young animal, consequently yield, in a given time, much less carbon and hydrogen in the corresponds to the oxygen taken up in the lungs. form adapted for the respiratory process than The substance of its organized parts would undergo a more rapid consumption, and would necessarily yield to the action of the oxygen, were not the deficiency of carbon and hydrogen supplied from another source. 'The continued increase of mass, or growth, the organs in the young animal, are dependent and the free and unimpeded development of on the presence of foreign substances, which, in the nutritive process, have no other function "It can hardly be doubted that the substance which is present in the gastric juice in a state of change is a product of the transformation of the stomach itself. No substances possess, in so high a degree as those arising from the progressive decomposition of the tissues containing gelatine, the property of exciting a change in the arrangement of the elements of other compounds. When the lining membrane of the than to protect the newly-formed organs from the action of the oxygen. It is the elements of these substances which unite with the oxygen; the organs themselves could not do so without being consumed: that is, growth or increase of mass in the body, the consumption of oxygen remaining the same, would be utterly impossible. The preceding considerations leave no doubt as to the purpose for which Nature has added to the food of the young of carnivorous mam-stomach of any animal, as, for example, that of malia substances devoid of nitrogen, which their organism cannot employ for nutrition, strictly so called, that is for the production of blood; substances which may be entirely dispensed with in their nourishment in the adult state. In the young of carnivorous birds, the want of all motion is an obvious cause of diminished waste in the organized parts; hence, milk is not provided for them. The nutritive process in the carnivora thus presents itself in two distinct forms, one of which we again meet with in the graminivora.' -pp. 68-70. the calf, is cleaned by continued washing with water, it produces no effect whatever, if brought into contact with a solution of sugar, with milk, or other substances. But if the same membrane be exposed for some time to the air, or dried, and then placed in contact with such substances, the sugar is changed, according to the state of decomposition of the animal matter, either into lactic acid, mannite and mucilage, or into alcohol and carbonic acid; while milk is instantly coagulated. An ordinary animal bladder retains, when dry, all its properties unchanged; but when exposed to air and moisture it undergoes a change not indicated by any obWe shall now attempt a sketch of the in-vious external signs. If, in this state, it be termediate steps in the processes by which nutrition is accomplished, which will include the chemistry of digestion and of the formation of the bile and urine, with the true function of the former fluid. We confine ourselves, here, to the carnivora, in whom the vital process is more simple.The food, consisting of compounds of proteine, is first dissolved into chyme in the This first process of digestion is one of the most interesting, but hitherto perhaps the most obscure, of the vital operations. Solution is effected by means of the gastric juice. But what is the solvent in that wonderful fluid? The answer is very simple-the gastric juice contains no solvent; and yet the food is dissolved. If the reader recollects what has been said of fermentation and metamorphosis, he will readily follow our author's explanation. stomach. The clear gastric juice contains a substance in a state of transformation, by the contact of which with those constituents of the food which, by themselves, are insoluble in water, the latter acquire, in virtue of a new grouping of their atoms, the property of dissolving in that fluid. During digestion, the gastric juice, when separated, is found to contain a free mineral acid, the presence of which checks all further change. That the food is rendered soluble quite independently of the vitality of the digestive organs has been proved by a number of the most beautiful experiments. Food, inclosed in perforated metallic tubes, so that it could not come into contact with the stomach, was found to disappear as rapidly, and to be as perfectly digested, as if the covering had been absent; and fresh gastric juice, out of the body, when boiled white of egg, or muscular fibre, were kept in contact with it for a time at the temperature of the body, caused these substances to lose the solid form and to dissolve in the liquid. placed in a solution of sugar of milk, that sub- In like manner, air is essential to digestion in the stomach, and is introduced by means of the saliva. 'During the mastication of the food, there is secreted into the mouth, from organs specially destined to this function, a fluid, the saliva, which possesses the remarkable property of enclosing air in the shape of froth, in a far higher degree than even soap-suds. This air, by means of the saliva, reaches the stomach with the food, and there its oxygen enters into combination, while its nitrogen is given out through the skin and lungs. The longer digestion continues, that is, the greater the resistance offered to the solvent action by the food, the more saliva, and consequently the more air, enters the stomach. Rumination, in certain graminivorous animals, has plainly for one object a renewed and repeated introduction of oxygu; for a more minute mechanical division of the food only shortens the time required for solution. The fact that nitrogen is given out by the skin and lungs is explained by the property which animal membranes possess of allowing all gases to permeate them, a property which can be shown to exist by the most simple experiments. A bladder, filled with carbonic acid, nitrogen, or hydrogen gas, if tightly closed and suspended in the air, loses in twenty-four hours the whole of the enclosed gas; by a kind of exchange, it passes outwards into the atmosphere, while its place is occupied by atmospherical air. A portion of intestine, a stomach, or a piece of skin or membrane, acts precisely as the bladder, if filled with any gas. This permeability to gases is a mechanical property, common to all animal tissues; and it is found in the same degree in the living as in the dead tissue. The blood, now charged with fresh fibrine and albumen, is sent to the lungs, whence it returns saturated with oxygen. This oxygen is conveyed, chiefly by the globules of the blood, to the minutest capillaries, where it contributes to the metamorphosis of existing tissues-in other words, to the change of matter. By this metamorphosis, certain parts of the living tissues lose the condition of vitality, and are resolved into new and lifeless, unorganised compounds, while a corresponding quantity of the fibrine and albumen of the blood supplies their place, assuming the structure of living tissues. To prevent the accumulaIt is known that in cases of wounds of the tion of the lifeless products, the blood is lungs a peculiar condition is produced, in which, by the act of inspiration, not only oxygen, but subjected to two processes, as it were, of atmospherical air, with its whole amount (four-filtration. In the kidneys the arterial blood fifths) of nitrogen, penetrates into the cells of the lungs. This air is carried by the circulation to every part of the body, so that every part is inflated or puffed up with the air, as with water in dropsy. This state ceases, without pain, as soon as the entrance of the air through the wound is stopped. There can be no doubt that the oxygen of the air, thus accumulated in the cellular tissue, enters into combination, while its nitrogen is expired through the skin and lungs. Finally, if we consider the fatal accidents which so frequently occur in wine countries from the drinking of what is called feather-white wine (der federweisse Wein), we can no longer doubt that gases of every kind, whether soluble or insoluble in water, possess the property of permeating animal tissues, as water penetrates unsized paper. This poisonous wine is wine still in a state of fermentation, which is increased by the heat of the stomach. The carbonic acid gas which is disengaged penetrates through the parietes of the stomach, through the diaphragm, and through all the intervening membranes, into the air-cells of the lungs, out of which it displaces the atmospherical air. The patient dies with all the symptoms of asphyxia caused by an irrespirable gas; and the surest proof of the presence of the carbonic acid in the lungs is the fact, that the inhalation of ammonia (which combines with it) is recognized as the best antidote against this kind of poisoning. Pp. 113-116. gives up those new products in which nitrogen predominates. These are uric acid, urea, and carbonate of ammonia. In the liver the venous blood is purified from those products in which the carbon prevails, and these may be represented by choleic acid, the chief constituent of bile. The matters secreted by the kidney being no longer available for any purpose in the body, are at once expelled. But with the bile it is far otherwise. function of the bile recognized as ascertainIn no previous work on physiology is the ed. It is viewed by some as an excretion; by others as assisting in digestion. But our author shows that it is no excretion, for in the carnivora the whole solid excrements do not contain a trace of bile, being composed entirely of inorganic matter, earth of bones, &c., while no bile can be found in the urine. Neither can the bile, owing to its composition, serve for the nutrition of the tissues. In fact, the whole of it returns into the circulation, and disappears entirely. It is consumed in the respiratory process, and is merely the vehicle of the carbon and hydrogen, which in that process unite with oxygen, and are given out from the lungs and skin as carbonic acid and water. Even in the carnivora, the quantity of bile daily secreted is very large-in a large dog, for example, 21 lbs.-yet not a trace is to be detected, as bile, in the excretions. Such is a brief sketch of the process of nutrition in the carnivora, and, were it only that the function of the bile is satisfactorily ascertained-that we now see in the bile the chief part of the fuel which serves for respiration and for producing the animal heatwere it only on this account, the volume before us would be full of interest to every physiologist. In the herbivora the process of the for mation of bile takes a somewhat different form. Here the change of matter could not yield more than a small fraction of the vast quantity of bile they secrete. A horse, for example, secretes 37 lbs. of bile daily (Burdach); and even in man, whose diet is mixed, from 17 to 24 ounces of bile are daily secreted. The products of the metamorphosis of the tissues, entering into new changes along with the elements of starch, sugar, &c, contribute to yield this enormous quantity of respiratory fuel; and here, also, the whole disappears, and is not to be traced in the excretions. The excrements of the horse contain, in one day, only a few ounces of matter which might be bile, but which, on examination, appears not to be 80. Horse-dung is chiefly composed of undigested woody fibre, and of saline mat ters. Professor Liebig very justly observes, Here, then, we have the chemical explanation of the process by which living tissue is converted into dead compounds. The blood, or rather the muscular fibre, which, having performed its functions, is to be removed, undergoes, with the aid of oxygen and water, a metamorphosis, the products of which are the chief constituents of bile and urine. The latter is at once expelled; the former returns into the circulation, and, being consumed or burned in the respiratory process, furnishes the animal heat. In carnivorous quadrupeds and in man the urate of ammonia disappears, its place being occupied by urea. Now, the profound researches of Liebig and Wöhler on uric acid have shown that by simple oxidation uric acid passes in urea and ca: bonic acid. This beautifully explains the difference between the urine of serpents and that of quadrupeds or man. In the latter, respiration is far more active, and hence their urine contains, at most, a trace of uric acid, while urea abounds in it. In serpents, with their sluggish respiration, the uric acid, or urate of ammonia, once formed, remains unchanged. A deficiency of oxygen, or, what amounts to the same thing, an excess of carbon, in the food of man, disturbs this arrangement; and the Gelatinous tissue is formed from blood, from consequence is, that a portion of the uric compounds of proteine. It may be produced by acid is not changed into urea, and calcuthe addition, to the elements of proteine, of al- lous disease ensues. Phthisical patients lantoine and water, or of water, urea, and uric acid; or by the separation from the elements of never suffer from calculus, because in them proteine of a compound containing no nitrogen. there is an excess of oxygen; while paThe solution of such problems becomes less dif- tients who, from a sedentary town-life, ficult, when the problem to be solved, the ques- have become affected with calculi of uric tion to be answered, is matured and clearly put. acid, no sooner go to the country and take Every experimental decision of any such ques- more exercise, than mulberry calculus (oxtion in the negative forms the starting-point of a new question, the solution of which, when ob- alate of lime) supervenes-oxalic acid betained, is the necessary consequence of our having, as Liebig and Wöhler have shown, an ing put the first question.'-pp. 143-144. that The experience of all those who have occupied themselves with researches into natural phenomena leads to this general result, that these phenomena are caused, or produced, by means far more simple than was previously supposed, or than we even now imagine; and it is precisely their simplicity which should most powerfully excite our wonder and admiration. intermediate product of the oxidation of uric acid along with urea; while that oxidation, if complete, would yield nothing but carbonic acid and urea. In wild carnivorous animals calculi are quite unknown, owing to their active habits. Fat food, which contains 70 or 80 per cent. of car Turning now to the chemical part of the above process, he proceeds to investigate, by the help of recent and most accurate analyses, what relations can be traced in regard to composition, between the blood on the one hand, and the secretions and ex-bon, favours the production of uric acid cretions on the other. Having first caused blood and muscle to be carefully analysed, he finds, as might now be expected, that they agree in composition. He then goes on to compare the formula thus obtained with that of choleic acid (bile) and with that of urate of ammonia (the solid urine of serpents and carnivorous birds.) It is surely very striking to find that the elements of the two latter, representing the bile and urine, when added together, exactly correspond to those of blood, with the addition of a little oxygen and water. calculus. Those animals which drink much water have no calculi, because a sufficient supply of water dissolves and removes the uric acid as fast as it is formed; and, finally, calculus, except as an imported disease, is unknown on the Rhine, because the Rhenish wines contain so much potash that the uric acid is kept dissolved by the alkali; while the wines of the south, which are deficient in potash, promote by their alcohol, acting in the same way as fat, the formation of uric acid. How important are these views in reference to so common and so dangerous a disease: and how probable is it that a rational application of them may serve greatly to assist in its prevention, or even in its cure! Another remarkable illustration of the influence of respiration, or of the supply of oxygen, on the urine, is found in our author's discovery, that the urine of stallfed cattle contains hippuric acid-an acid with 18 equivalents of carbon; while the urine of the same animals, when living in the fields, or compelled to labour, does not yield a trace of hippuric acid, but only benzoic acid, with only 14 equivalents of carbon. The difference is consumed in respiration. The section of the work now under consideration contains many other beautiful examples of the close chemical relation between the tissues of the body and the secretions or excretions. Thus, it is ex plained that proteine, by very simple chemical reactions with other compounds present in the body, may be made to yield hippuric acid, gelatine, or allantoine (the peculiar principle of the urine in the foetal calf); that the blood, with a certain amount of oxygen, may yield not only, as above stated, urate of ammonia and choleic acid, but, as occurs in the herbivora,hippuric acid,choleic acid, urea, ammonia, and water-or, increasing the supply of oxygen benzoic acid, choleic acid, urea, carbonic acid, and water : they agree with observation in many cases, and in all are founded on very careful experiments. We would again remind the reader of the analogy between these supposed transformations and the metamorphosis of sugar into carbonic acid and alcohol. The author terminates this section with the following conclusion, drawn from a comparison of all the facts known in regard to the food, the secretions, and the excretions of the herbivora, namely: That if the elements of proteine and starch, oxygen and water being present, undergo metamorphosis, and mutually affect each other, we may obtain, in certain circumstances, as the products of this complex metamorphosis, choleic acid, urea, ammonia, and carbonic acid, and besides these no other product whatever.' Soda is essential to the formation of bile in the herbivora; and as they secrete an immense quantity of bile, they require a large supply of salt. If there be a deficiency of soda, proteine, with water and oxygen, will yield no bile, but only fat, urea, and carbonic acid. This is the reason why an animal cannot be fattened if too abundantly supplied with salt. bile amounts to five or six times the quantity of that contained in the daily amount of metamorphosed tissue, or what is the same thing, five or six times the carbon of the daily waste of matter. the proteine in their food, which supplies Hence the contribute to the formation of bile. Furstarch, &c., of their food must necessarily In this class of animals the carbon of the and that proteine with a little water may yield gelatine and choloidic acid (one of the acids of the bile); while again proteine, added to uric acid, urea, and water, may yield gelatine.* We cannot quote the de-ther, in consequence of the large amount tails; but although professedly hypotheti- of soda required for their bile, the urine of cal, and intended chiefly as a means of pro- that of the carnivora contains but little. the herbivora is loaded with soda, while moting the study of this curious subject, we cannot help thinking that there is much On the other hand, the urine of the latter is rich in phosphates, which occur in very small proportion in that of the former; the phosphoric acid in their food, which is not abundant, being retained to assist in the formation of the bones and of the substance actual truth in these chemical statements : Such of our readers as are familiar with the chemical works of the day will understand that these relations are best expressed in the form of equations, in which chemical symbols or abbreviations are employed. The system of notation adopt-of the brain and nerves. ed by the author is extremely simple and clear, but we do not quote his equations, because the explana-tened, and that only when they are stallIt is only the herbivora that can be fattions necessary for understanding them may not be within the reach of many readers, and would, if given here, occupy too much space. We have preferred, therefore, attempting to describe these interesting coincidences of composition in as few words as possible. The principle to be borne in mind is, any given number of atoms or equivalents f certain elements admits of many different arrangements, each of which may yield a new compound, or a new group of compounds, the sum of the elements in each group or arrangement remaining the same. This principle has been long known and constantly applied in explaining the changes which occur in inorganic chemistry: it is here extended, with the aid of exact analyses, to the more complex changes in the animal body. that fed. In the wild state, they become full and plump, but not fat, as is seen in the deer and hare, while the carnivora have always lean and sinewy muscles. Cattle, when confined, and fed on food containing much starch, &c., are in the best circumstances for becoming both fleshy and fat. Their organism possesses the power of assimilating, or converting into animal tissue, all the compounds of proteine in their food; while the starch, &c., respiration being checked, cannot be entirely converted into bile, or |