1847] Origin and Uses of the Bile. 139 until the Reports he produced at the instigation of that valuable institution, "The British Association for the Advancement of Science," disclosed him as a great practical philosopher and admirable genius. He is now the spoken-of of all men, even to the fathering upon him views and doctrines he never entertained. That his reputation is soundly based and will prove durable we can have no doubt; for, although some of his views are by no means so original as his most ardent admirers would have us believe, (and here we cannot but protest against the non-acknowledgment of Dr. Prout's priority in respect to certain of these,) and some are very hypothetical; yet, in the firm establishment of others of immense importance, in his expanded idea of chemical science, in his happy generalizations and lucid descriptions, in the light he has thrown upon various departments of physiology, and the remarkable impulse he has communicated to agricultural improvement and chemical investigation, Liebig has acquitted himself with a rare ability, and has conferred lasting benefit upon mankind. The present part of the new edition of the "Animal Chemistry" is indeed an excellent indication of the claims of its author; containing, as it does, so many exemplifications of the correctness of the views already advanced by him, and so little in qualification of them. It is, in fact, so extended by the new matter illustrative of "the Chemical Process of Respiration and Nutrition," and by the addition of an entirely new section upon the method in which the investigation of the Metamorphoses of Animal Tissues" should be pursued, that it may, as the Editor justly remarks, be almost considered as a new work. The general views of the author upon Respiration and Nutrition are too familiarly known to our readers to admit of our adverting to them in this notice, otherwise than by citing one or two of the additional illustrations which he brings forward; and we shall chiefly confine our attention to the new section, which indeed occupies nearly a hundred pages of the present part. Our first extract shall be taken from an interesting sub-section upon the origin and uses of the Bile. "The taking up of dissolved foreign matters into the blood, or the absorption of such matters, is a chemico-mechanical act, which, as we have seen, extends to liquid substances of every kind, saline solutions, poisons, &c. It is now therefore obvious that, by the forcible entrance of arterial blood into the capillary vessels, the fluids contained in these-in other words, the soluble compounds produced by the transformation of the organized tissues-must, as above stated, be compelled to move towards the heart. These compounds cannot be employed for the reproduction of those tissues from which they are derived. They pass through the absorbent and lymphatic vessels into the veins, where their accumulation would speedily put a stop to the nutritive process, were it not that this accumulation is prevented by two contrivances adapted expressly to this purpose. "A part of the venous blood, before reaching the heart, is made to pass through the liver: a part of the arterial blood, on the other hand, passes through the kidneys, which separate from it all substances incapable of contributing to nutrition. Of the newly produced compounds, some are collected in the urinary bladder; another part is separated by the liver in the form of Bile. Physiolo gists cannot entertain any doubt as to the origin of the constituents of the Urine and of the Bile. Even when all food is withheld, the secretion of bile takes place : in the bodies of those who have been starved to death, the gall-bladder is found distended and full of bile. "It is obvious that the constituents of the urine, as well as the chief constituents of the bile, are products of the transformation of the blood and of the organized tissues. The elements of urea, uric acid, and bile, were previously constituent elements of the living tissues, which have lost the condition of life in the vital process by the action of external causes. We know with certainty, therefore, that some of the nitrogenized compounds, produced by the metamorphosis of organized tissues, after being separated from the arterial blood by means of the kidneys, are expelled from the body as utterly incapable of farther alteration. "But another nitrogenized chief product, in which we find the sulphur of the transformed tissues, and which is peculiarly rich in carbon, returns, as bile, during the progress of digestion, into the system, in which it gradually disappears, partially or entirely. If we compare the composition of the bile with the nature and composition of the substances which are expelled through the intestinal canal, it evidently appears, that the combustible elements of the bile, without referring to the important part which that fluid plays in the process of digestion, ultimately leave the body in the shape of oxidized compounds, and are perfectly capable of being employed in respiration. "The bile contains sulphur and is a compound of soda. The fæces of carnivorous animals, as of serpents and of dogs, fed with flesh and bones, contain a very small proportion of organic excretions, which promote the passage through the intestine of the substances not taken up during the digestive process. They consist chiefly of bone earth, and, when incinerated, yield only traces of soluble salts, among which, however, is not found carbonate of soda, which is left when bile is incinerated. It is perfectly certain the soda of the bile has again entered into the circulation. We find the soda and sulphur of the bile, the first in the form of a salt of soda, the latter in the form of a sulphate, in the urine. "The peculiar property of the vessels of the intestinal canal, that of taking up and carrying into the blood soluble substances of every kind, provided these do not form an insoluble compound with the organic tissues of the vessels, is well-known. A solution of common salt (1 part to 80 of water) administered as an enema, disappears in the intestine just as pure water would do, without the proportion of salt in the fæcal evacuation an hour after being in the smallest degree increased. But the proportion of salt in the urine increases in a direct proportion. In like manner, ferrocyanide of potassium, or iodide of potassium, introduced in the same way into the rectum, very soon appears in the urine; and the disappearance of an enema of bile in the rectum, while the bile cannot be detected in the urine, proves, not only the passage or return of the bile into the blood, but also its employment in the respiratory process." P. 73-77. Employment of Alcohol in Respiration.-The alcohol of fermented liquors plays the same part in the body of man as the non-nitrogenized constituents of his food; for although its elements do not of themselves possess at the temperature of the body the property of combining with oxygen, yet brought into contact with other bodies during their eremacausis or absorption of oxygen, which are always present in the body, it acquires the property in a higher degree than 'fat or other non-nitrogenized substance. "When cod-liver oil is administered to persons accustomed to drink daily a certain quantity of wine, it often happens, that the inclination for wine is diminished, so that at last they can take no wine at all: obviously, because alcohol and fat oil in this case mutually impede the excretion of each other through the skin and lungs, since the body does not assimilate the fat. This may also possibly be the reason why most people find that they can take wine with animal food, but not with farinaceous or amylaceous food." P. 97. 1847] The Respiratory Elements of Food. 141 Experiments prove that neither the urine nor the condensed fluid of expired air contain alcohol, whence it necessarily follows that its elements have been given out as oxidized products, its carbon as carbonic acid, and its hydrogen as water. When, however, the supply of oxygen is defective, the amount of the carbon of the alcohol being greater than that of the oxygen necessary for its conversion, "the alcohol must then pass off as such, or in the form of a lower stage of oxydation, as butyric or acetic acid: or else it must be discoverable in the body." The agency of alcohol as a respiratory element of food is illustrated by the following anecdote : "In England, servants receive daily a certain amount of Beer, or in the case of Total Abstinence, its equivalent in money. A friend informs me that in a certain household it was observed, that, from the day on which the servants ceased to receive beer from their master, the consumption of bread increased in a ratio corresponding to the diminution of beer; so that the beer was twice paid for, once in money, and the second time in the form of an equivalent of another kind of food, yielding the same amount of carbon and hydrogen." P. 98. There is an interesting section upon the derivation of the various vegetable acids and starch, gum, &c. from the carbonic acid of the plant, and their reconversion into this in the animal; but, as abridgment is impossible, we content ourselves with a single extract. Respiration an indirect Combustion." In vegetables, sugar has thus been formed from Carbonic Acid, by the separation of Oxygen, and by the introduction of Hydrogen in its place. In the animal organism, the process is reversed: the hydrogen, in the animal body, is removed and replaced by Oxygen; and in this way the Carbon again assumes its original form of combination. "This is, generally speaking, the essential character of the process of eremacausis or respiration it is an indirect process of combustion, going on at a low temperature, and with a limited supply of Oxygen. We are not acquainted with any case in which, under these circumstances, the Carbon of an organic substance combines directly with Oxygen to produce carbonic acid. No combustion of the carbon, in the proper sense of the word, takes place, but the Hydrogen of the compound is oxidized and separated as Water, while its equivalent of oxygen is taken up in its place. Should one of the intermediate compounds, which are formed by the gradual replacement of the Hydrogen by Oxygen, possess, in itself, an attraction for Oxygen, then for 1 eq. Hydrogen more than 1 eq. Oxygen is taken up. The development of heat in the respiratory process, therefore, depends not on the direct oxidation of the Carbon but on the conversion of the Hydrogen of the organic compound into water, and on the substitution of one or more equivalents of Oxygen for this Hydrogen." P. 110. The Elements of Respiration as Sources of Heat.-The amount of heat produced in their oxidation varies much in these different constituents of food, being greater in proportion as they are rich in combustible or unoxidized Hydrogen-that being the substance during the combination of which with oxygen most heat is extricated. Estimating the heat produced during oxidation by the amount of oxygen required for converting different substances into carbonic acid and water, we find that 1b of Sugar of Milk combines with 187 volumes of oxygen; the same quantity of Cane Sugar with 196: of Starch with 207; of Alcohol with 362; and of Fat with 511 volumes. If 1 part of Sugar of Milk can keep up the normal temperature for 33 hours, the same quantity of Cane Sugar, Starch, Alcohol, and Fat, will maintain it for 35, 36, 65 and 87 hours respectively. In order to keep the body at the same temperature during equal times, there are required, of Cane Sugar 100 parts, Grape Sugar 106, Starch 97.2, Alcohol 53.8, Fat 40-2, and Flesh 309.7. Pure flesh, therefore, possesses the smallest, and fat the greatest value as an Element of Respiration." The Intestinal Canal an Organ of Secretion. "It is hardly to be doubted that when nitrogenized substances are to be found in the fæces, and their presence has been demonstrated by all the analyses hitherto made, these substances can only be, either products of the change of matter in the intestinal canal itself, or products of the general change of matter, which have not undergone the normal changes, and which are separated from the blood, in virtue of a power belonging to the intestinal canal, or to some portion of it. The apparent deficiency or absence of any structure in the canal, by means of which the secretory process is effected, is opposed to the opinion, that a true circulation, attended by a restoration of the disturbed equilibrium in the organism, goes on there but the following considerations may perhaps serve as a support to that opinion. "It is plain that the secretory effect of the canal, the amount of matters separated from the blood by its action, must stand in a definite ratio to the amount of oxygen taken up and consumed by the individual: or, what comes to the same thing, to the amount and composition of the food. Every change in the relative proportion of blood-constituents and non-nitrogenized elements of respiration in the food, must exert an influence on the quantity and composition of the fæces. "If we assume, that the food contains a larger proportion of blood-constituents than is required for the supply of the waste of matter in the body, then the excess of these constituents must augment the mass of blood, or, if the animal possess the necessary assimilative power, the mass of flesh in the body. If the amount of oxygen taken up be exactly sufficient to convert into oxidized products in a given time the products of the change of matter present in the system, as well as the elements of respiration contained in the food, then the fæces must possess the normal composition and character. But if the amount of sugar or of fat introduced in the food be greater than the oxygen supplied in an equal time can completely convert into carbonic acid and water, then, in an animal possessed of the necessary power, a part of the sugar will be converted into fat; and this fat, along with the fat introduced in the food, will go to increase the quantity of fat in the body. If we now suppose the products of the change of matter and non-nitrogenised elements of respiration possess an equal attraction for the oxygen with which they combine in the organism, it is evident that the oxygen present must be divided between them. A certain portion will unite with the sugar, or with the elements of non-nitrogenized elements of respiration: another portion will combine with the elements of the nitrogenized products resulting from the change of matter. When the supply of oxygen is deficient, or, what comes to the same thing, when there is an excess of non-nitrogenized and nitrogenised elements of respiration (the latter being always viewed as the products of the change of matter), their normal conversion into oxidized compounds must necessarily appear impeded. "Sugar, when oxygen is wanting, may pass into fat: but only a part of the products of the change of matter can be, under these circumstances, converted into the normal oxidized compounds. While, in the normal state of nutrition, of waste and restoration, and of the supply of oxygen, the nitrogen of the effete 1847] Influence of Variety of Food. 143 tissues takes the form of urea, and the sulphur of the bile that of sulphuric acid, which are discharged in the urine; when there is a deficiency of the oxygen necessary to the formation of these products, uric acid, a compound much richer in carbon than urea, will be formed, a part of the sulphur will appear in the urine as cystine (cystic oxide), or in some other form; and the excess of the products of the change of matter which has not undergone these changes, must either remain in the blood, or it must, as we know of no other exit for it, be evacuated by the intestinal canal." P. 144-146. It will be probably more convenient to notice Dr. Thomson's interesting little work upon "The Food of Animals," before giving any further account of the one we are occupied with. It consists in the description of a series of well-contrived experiments upon the comparative value of various articles of diet in furnishing supplies of milk to cows, and is consequently of more immediate interest to the agriculturist than to the medical reader. Still, being the work of an accomplished chemist and physician, it contains several incidental observations of value to the practitioner, to some of which we will allude. Upon the whole, the book is an admirable exemplification of the great practical advantages derivable from pursuing the track of investigation so lucidly indicated by Liebig. Influence of Variety of Food on Milk, and on Man.-Several series of experiments proved in a decided manner that, upon a change of food, the amount of milk produced became increased, diminishing again after the same diet had been continued for some days. "That a change of diet is necessary for animals which are kept in a confined condition, is proved by the tables previously given, in a striking manner, and the results now obtained amply sustain the idea supported by me some time ago in reference to the dietary of human beings shut up in poor-houses and places of confinement. It was then argued that in order to retain the human constitution in a healthy condition, variety of food should be properly attended to,' and different species of diet were suggested as well calculated to supply a series of dishes to the poor. In the Asylum for the Houseless, and in the House of Refuge at Glasgow, the recommendations were followed out; and, according to the report of the treasurer, 'the dinner meals being varied two or three times a week, the change in the dietary routine is much relished by the inmates, and may have had some effect in the greater degree of health which has been evident among them of late.' (Proceedings of Phil. Soc. of Glasgow, Vol. 1, p. 40). The analogy subsisting between the physical nature of human beings and of many of our domestic animals would lead us to the conclusion, upon physiological grounds, that the dietary should be conducted upon precisely the same principles. To prove this by exact experiment is a point, it will be admitted, of considerable importance to the agriculturist, although it may have been, as might be expected, surmised by many intelligent observers. Not only, however, is a variety of food requisite for an animal in an artificial state, it is found also to be beneficial to one in a condition more akin to that of nature. For it is upon this principle we are able to account for the superior influence of old natural pastures, which consist of a variety of grasses and other plants, over those pastures which are formed of only one grass, in the production of fat cattle and good milk cows. To any one who considers with attention the experiments which have been detailed, there cannot remain a doubt in the mind that cattle, and especially milk cows, in a state of confinement, would be benefited by a very quent and entire change in their food. It might not be too much to say that a daily modification in the dietary of such animals would be a sound scientific fre |