used in respiration. It is from this source | mal products is gelatine. It constitutes the that fat is derived. We do not remember to have met with a more beautiful instance of adaptation to circumstances than this of the production of fat in stall-fed animals, considered in relation both to its cause and its effect; and for the development of this curious subject we are indebted to the sagacity of Professor Liebig. He first directs atttention to the composition of starch and sugar, in which carbon is to hydrogen as 43 to 6 nearly in 100 parts, the rest being oxygen; while the proportion of these elements in fat is 79 to 11 nearly-in other words, the same. From this he concludes that the only way in which starch can pass into fat is by a loss of oxygen; and, in fact, if we subtract from the composition of starch a certain amount of oxygen, the remainder will express exactly the proportion of the elements in fat. Now the direct cause of the production of fat is a deficiency of oxygen, so that the separation of fat tends directly to make up for the deficiency which caused it; and the growth of fat in a sedentary man, or in a stall-fed animal, is a beautiful provision of nature to furnish from another source the oxygen which respiration ought to have supplied, and which is required to keep up the animal heat. The author has, we think, succeeded in proving the existence of a very close connection between the formation of fat and the respiratory process, and he gives a very interesting explanation of the various means resorted to for fattening animals; all of which, although hitherto empirical, admit of the most satisfactory elucidation on the principles here indicated. Thus, Experience teaches us that, in poultry, the maximum of fat is obtained by tying the feet and by a medium temperature. These animals, in such circumstances, may be compared to a plant, possessing in the highest degree the power of converting all food into parts of its own structure. The excess of the constituents of blood forms flesh and other organized tissues, while that of starch, sugar, &c., is converted into fat. When animals are fattened on food destitute of nitrogen, only certain parts of their structure increase in size. Thus, in a goose fattened in this method, the liver becomes three or four times larger than in the same animal when well fed with free motion; while we cannot say that the organized structure of the liver is thereby increased. The liver of a goose fed in the ordinary way is firm and elastic; that of the imprisoned animal is soft and spongy. The difference consists in a greater or less expansion of its cells, which are filled with fat.'-p 94. One of the most remarkable of the ani mass of the skin, of most membranes, and of the organic part of the bones. But it differs from fibrine, albumen, and caseine in this, that, although formed from proteine, it cannot, like these substances, be made again to yield proteine. Once formed, gelatine no longer belongs to the series of compounds of proteine. The consequence of this is, that it is altogether incapable of yielding blood, or consequently of contributing to the growth or nutrition of the fibrous or other tissues which contain proteine. Animals fed exclusively on gelatine soon die with all the appearances of starvation. Yet there is no doubt that, when mixed with other animal food, it serves some purpose in the economy; for dogs eat bones, and the gelatine is not to be found in their excretions. Besides, the uniform experience of medical men proves that food composed principally of gelatine, such as strong soup or jelly, is most advantageous as an article of diet for convalescents. There has lately occurred in Paris a controversy on the use of the gelatine of bones for hospital soup, as recommended by D'Arcet, and the most contradictory opinions as to its qualities are daily published. Professor Liebig has, we think, decided this question. He has shown that gelatine cannot yield blood, and that by itself, therefore, it cannot support life. But he supposes that it is dissolved in the stomach, and, being conveyed in the blood to every part of the body, acts as nutriment to the gelatinous membranes and bones alone. This ingenious idea explains both how gelatine mixed with other animal matter forms a good diet; and how it is peculiarly adapted for the sick and convalescent, in whom it acts by giving nutrition to the gelatinous tissues, and so sparing much of the energy of the enfeebled digestive system, which is thus not consumed in producing gelatine for these tissues, but is expended in the digestion of sanguiferous nourishment. We can now readily credit the statements of D'Arcet, who has shown that in all the hospitals where the gelatine of bones has been used as a principal, but not the only, article of animal food, the patients relish it, the success of the treatment has been much increased, and the much diminished. Now that we possess period of convalescence on the average what appears to be the true theory of the action of gelatine, it is to be hoped that the prejudice, previously very natural, which exists in this country against its use, may be overcome, and that our hospitals may participate in the benefits of D'Arcet's | severe muscular exertion. Thus the chief benevolent system, which, when success-objects of our agriculture are found to be fully conducted, has likewise the advantage those substances which are most effectual, of superior economy. The food best adapted for man is that which contains a due mixture of azotised matter (fibrine, albumen, &c.), and nonazotised matter (sugar, starch, &c.). Hear our author : 'A nation of hunters, on a limited space, is utterly incapable of increasing its numbers beyond a certain point, which is soon attained. The whole of the carbon necessary for respiration must be obtained from the flesh of animals, of which only a limited number can find food on the space supposed. But 15 lbs. of flesh contain not more carbon than 4 lbs. of starch; and while the savage, with one animal and an equal weight of starch, could support life and health for a certain number of days, he would be compelled, if confined to flesh alone, in order to procure the carbon necessary for respiration and for the animal heat, to consume five such animals in the same period. even when taken alone, in supporting animal life. The potato is not to be forgotten. It is not so rich in fibrine as wheat-flour, but it has enough, with the starch or respiratory matter it contains, to be a most valuable article of diet. We must briefly notice another very interesting section of this work. It is that which treats of the action of medicines and poisons on the system. The first class of such agents is that of substances which produce a very marked effect, without their elements taking a direct share in the changes which ensue. These bodies originate as it were an action, which is subsequently propagated from particle to particle. They are uniformly substances in a state of change or transformation, and appear to act on the blood 'It is easy to see, from these considerations, as yest does on a solution of sugar. In this how close the connection is between agriculture class appear miasms, contagions, and the and the multiplication of the human species. singular sausage poison of Wurtemberg. The cultivation of our crops has ultimately no The latter is an excellent sample. Sausaother object than the production of a maximum of those substances which are adapted for assi- used in that country. When ill-prepared, ges, made in a peculiar way, are much milation and respiration in the smallest possible space. Grain and other nutritious vegetables they become poisonous, and their effects yield us, not only in the form of starch, &c., the are invariably fatal. The patient graducarbon which protects our organs from the action ally dries up into a sort of mummy, and, of oxygen, and serves to produce also the heat after weeks or months of misery, death essential to life, but also, in the form of vegetable closes the scene. But there is no poisonfibrine, albumen, and caseine, our blood, from ous substance to be detected in the sausage. which all the other parts ofthe body are developed. It is, according to our author, in a peculiar 'Man, when confined to animal food, respires, like the carnivora, at the expense of the matters state of fermentation, which is not checkproduced by the metamorphosis of organised ed by the action of the stomach, and which tissues: and, just as the lion, tiger, and hyena, in the cages of a menagerie, are compelled to accelerate the waste of the organised tissues by incessant motion, in order to furnish the matters necessary for respiration and for animal heat, so the savage, for the same object, is forced to make the most laborious exertions, and to go through a vast amount of muscular exercise. He is compelled to consume force, merely in order to supply matter for respiration. unfortunately is communicated to the blood. It never ceases till every part ca pable of solution has been destroyed, and death, of course, must follow. But, as it appears that the poisonous sausage may be rendered quite safe by boiling, and by other simple means of arresting fermentation, we may hope that the true theory of the poison will lead to a successful treatCultivation is the economy of force. ment of this frightful accident, which unThe unprofitable exertion of power, the waste of force in agriculture, in other branches of in happily is very frequent. Miasms and condustry, in science, or in social economy, is char-tagions act on the very same principle; acteristic of the savage state, or of the absence of cultivation.'-pp. 76—78. Nature furnishes one substance in the animal kingdom which is perfectly fitted to sustain life. It is milk, a mixture of caseine, sugar, fat, and salts, with water. It is curious that the nearest approach to this in artificial food is bread, which is a mixture of vegetable fibrine (gluten) and starch, along with salts. Bread and water, it is well known, will support life permanently. Flesh will do so likewise-with the aid of and the reason that all are not affected by them seems to be, that they require the presence of a peculiar compound in the blood, which enters into decomposition, and when the whole of this peculiar matter is destroyed, the disease disappears. If there be much, the case is severe-if little, the case is mild; and apparently, in many contagious diseases, the peculiar decomposible matter, once destroyed, can never be renewed; so that these diseases occur but once. The second class of these agents consists 'A similar relation exists in the case of the of those whose elements take a share in peculiar principle of asparagus and althæa, the changes produced. This class is sub-asparagine; which also, by the addition of oxydivided into orders, of which the first in-gen and the elements of water, yields the elements of taurine.* cludes the metallic poisons. These enter directly into combination with the tissues, and if the vital force cannot destroy the compounds thus formed, death ensues. The second order contains empyreumatic and antiseptic substances, which act by checking the vital transformations; just as, out of the body, they check fermentation or putrefaction. The third order consists of substances whose elements take a share in certain vital processes of secretion or excretion, and thus excite abnormal appearances, either accelerating, disturbing, or retarding the functions. These may be divided into azotised and non-azotised. It is very remarkable that no medical agent devoid of nitrogen is poisonous in moderate quantity; while those containing nitrogen, all except three, are poisonous in a very small dose. This last division includes the vegetable alkalis, morphia, quinine, strychnia, &c. Professor Liebig remarks that— 'We shall never be able to discover how men were led to use the infusion of a certain leaf (tea), or the decoction of a certain seed (coffee). But some cause there must be, which has induced whole nations to make the practice a necessary of life. And it is surely still more remarkable, that the peculiar effects of both plants on the health must be ascribed to one and the same substance; the presence of which in two vegetables belonging to different natural families, and the produce of different quarters of the globe, could hardly have presented itself to the boldest imagination. Yet recent researches have demonstrated that caffeine, the active principle of coffee, and théine, that of tea, are, in all respects, perfectly identical. It is not less worthy of notice, that the American Indian, living entirely on flesh, discovered for himself, in tobacco smoke, a means of retarding the change of matter in the tissues of his body, and thereby of making hunger more endurable; and that he cannot withstand the action of brandy, which, acting as an element of respiration, puts a stop to the change of matter by performing the function which properly be longs to the products of the metamorphosed tissues, when the diet is entirely animal. Tea and coffee were originally met with among nations whose diet is chiefly vegetable. Without entering minutely into the medicinal action of caffeine (theine), it will surely appear a most striking fact, even if we chose to deny its influence on the process of secretion, that this substance, with the addition of oxygen and the elements of water, can yield taurine, the nitrogenised compound peculiar to bile. 'The addition of the elements of water and of a certain quantity of oxygen to the elements of theobromine, the characteristic principle of the cacao-bean (theobroma cacao,) yields the elements of taurine and urea, of taurine, carbonic acid, and ammonia, or of taurine and uric acid. To see how the action of caffeine, asparagine, theobromine, &c., may be explained, we must call to mind that the chief constituent of the bile contains only 3.8 per cent. of nitrogen, of which only the half, or 1.9 per cent., belongs to the taurine. 'Bile contains, in its natural state, water and weight of the former to 10 of the latter. If solid matter, in the proportion of 80 parts by we suppose these 10 parts by weight of solid matter to be choleic acid, with 3.87 per cent. of nitrogen, then 100 parts of fresh bile will contain 0.171 parts of nitrogen in the shape of taurine. Now this quantity is contained in 0.6 parts of caffeine; or 2 8-10 grains of caffeine can give to an ounce of bile the nitrogen it contains contain no more than 1-10th of a grain of caffeine, still, if it contribute in point of fact to the formation of bile, the action, even of such a quantity, cannot be looked upon as a nullity. Neither can it be denied that, in the case of an excess of non-azotised food and a deficiency of motion, which is required to cause the change of matter in the tissues, and thus to yield the nitrogenised product which enters into the composition of the bile-that in such a condition, the health may be benefited by the use of compounds which are capable of supplying the place of the nitrogenised product formed in the healthy state of the body, and essential to the production of an important element of respira tion. In a chemical sense-and it is this alone which the preceding remarks are intended to show-caffeine or theine, asparagine, and theobromine, are, in virtue of their composition, better adapted to this purpose than all other nitrogenised vegetable principles. The action of these substances, in ordinary circumstances, is not obvious, but it unquestionably exists. in the form of taurine. If an infusion of tea With respect to the action of the other nitrogenised vegetable principles, such as quinine, or the alkaloids of opium, &c., which manifests itself, not in the processes of secretion, but in different phenomena, physiologists and pathologists entertain no doubt that it is exerted chiefly on the brain and nerves. This action is commonly said to be dynamic-that is, it accelerates, or retards, or alters in some way, the phenomena of motion in animal life. If we reflect that this action is exerted by substances which are material, tangible, and ponderable; that they We omit the elaborate tables of equations appended to these statements. They would only be intelligible to readers who are sure to study the original work. disappear in the organism; that a double dose | product, before a certain number of its elements acts more powerfully than a single one; that, can become constituents of the nervous matter; after a time, a fresh dose must be given, if we and it must be considered as quite certain, that wish to produce the action a second time,-all a product of the vital process in a plant, introthese considerations, viewed chemically, permit duced into blood, will, if its composition be adapted only one form of explanation: the supposition, to this purpose, supply the place of the first, senamely, that these compounds, by means of cond, or third product of the alteration of the their elements, take a share in the formation of compound of proteine. Indeed it cannot be new, or the transformation of existing, brain considered merely accidental, that the composiand nervous matter. tion of the most active remedies, namely, the vegetable alkaloids, cannot be shown to be re except only the substance of the nerves and brain. All these remedies contain a certain quantity of nitrogen, and, in regard to their composition, they are intermediate between the compounds of proteine and the fats. However strange the idea may, at first sight, appear, that the alkaloids of opium or of cin-lated to that of any constituents of the body, chona bark, the elements of codeine, morphia, quinine, &c., may be converted into constituents of brain and nervous matter, into organs of vital energy, from which the organic motions of the body derive their origin; that these substances form a constituent of that matter, by the remo- 'In contradistinction to their chemical characval of which the seat of intellectual life, of sen- ter, we find that the substance of the brain exsation, and of consciousness, is annihilated: it hibits the characters of an acid. It contains far is, nevertheless, certain, that all these forms of more oxygen than the organic bases or alkapower and activity are most closely dependent, loids. We observe, that quinine and cinchonine. not only on the existence, but also on a certain morphia and codeine, strychnia and brucia, quality of the substance, of the brain, spinal which are, respectively, so nearly alike in compomarrow, and nerves; insomuch, that all the mani-sition, if they do not produce absolutely the same festations of the life or vital energy of these modifications of nervous matter, which are recognized as the phenomena of motion, sensation, or feeling, assume another form as soon as their composition is altered. The animal organism has produced the brain and nerves out of compounds furnished to it by vegetables: it is the constituents of the food of the animal, which, in consequence of a series of changes, have assumed the properties and the structure which we find in the brain and nerves. 'If it must be admitted as an undeniable truth, that the substance of the brain and nerves is produced from the elements of vegetable albumen, fibrine, and caseine, either alone, or with the aid of the elements of non-azotised food, or of the fat formed from the latter, there is nothing absurd in the opinion that other constituents of vegetables, intermediate in composition between the fats and the compounds of proteine, may be applied in the organism to the same purpose. Brain and nervous matter is, at all events, formed in a manner similar to that in which bile is produced; either by the separation of a highly nitrogenised compound from the elements of blood, or by the combination of a nitrogenised product of the vital process with a non-azotised compound (probably, a fatty body.) All that has been said in the preceding pages on the various possible ways by which the bile might be supposed to be formed, all the conclusions which we attained in regard to the co-operation of azotised and non-azotised elements of food, may be applied with equal justice and equal probability to the formation and production of the nervous effect, yet resemble each other in their action more than those which differ more widely in composition. We find that their energy of action diminishes, as the amount of oxygen they contain increases (as in the case of narcotine), and that, strictly speaking, no one of them can be entirely replaced by another. There cannot be a more decisive proof of the nature of their action than this last fact: it must stand in the closest relation to their composition. If these compounds, in point of fact, are capable of taking a share in the formation or in the alteration of the qualities of brain and nervous matter, their action on the healthy as well as the diseased organism admits of a surprisingly simple explanation. If we are not tempted to deny, that the chief constituent of soup may be applied to a purpose corresponding to its composition in the human body, or that the organic constituent of bones may be so employed in the body of the dog, although that substance (gelatine in both cases) is absolutely incapable of yielding blood; if, therefore, nitrogenised compounds, totally different from the compounds of proteine, may be employed for purposes corresponding to their composition; we may thence conclude that a product of vegetable life, also different from proteine, but similar to a constituent of the animal body, may be employed by the organism in the same way and for the same purpose as the natural product, originally formed by the vital energy of the animal organs, and that, indeed, from a vegetable substance. The time is not long gone by when we had not the very slightest conception of the cause of the various effects of opium, and when the action of cinchona bark was shrouded in incomprehensible obscurity. Now that we know that these effects are caused by chrystalizable compounds, which differ as much in composition as in their action on the system; now that we know the substances to which the medicinal or poisonous energy must be ascribed, it would argue only want of sense to consider the action of these substances inexplicable; and to do so, as many have done, because they act in very minute, he proceeds to investigate; and in a most doses, is as unreasonable as it would be to judge of the sharpness of a razor by its weight. Thus, as we may say, in a certain sense, of caffeine or theine and asparagine, &c., as well as of the non-azotised elements of food, that they are food for the liver, since they contain the elements by the presence of which that organ is enabled to perform its functions, so we may consider these nitrogenised compounds, so remarkable for their action on the brain and on the substance of the organs of motion, as elements of food for the organs as yet unknown, which are destined for the metamorphosis of the constituents of the blood into nervous substance and brain. Such organs there must be in the animal body, and if, in the diseased state, an abnormal process of production or transformation of the constituents of cerebral and nervous matter has been established; if in the organs intended for this purpose the power of forming that matter out of the constituents of blood, or the power of resisting an abnormal degree of activity in its decomposition or transformation, has been diminished; then, in a chemical sense, there is no objection to the opinion, that substances of a composition analogous to that of nervous and cerebral matter, and, consequently, adapted to form that matter, may be employed, instead of the substances produced from the blood, either to furnish the necessary resistance, or to restore the normal condition. 'An accurate investigation would probably discover differences in the composition of the brain, spinal marrow, and nerves. According to the observations of Valentin, the quality of the cerebral and nervous substance is very rapidly altered from the period of death, and very uncommon precautions would be required for the separation of foreign matters, not properly be longing to the substance of the spinal marrow or brain. But, however difficult it may appear, the investigation seems yet to be practicable.'pp. 178-190. We consider these hints of the author's, for they are no more, on a most obscure subject, as worthy of careful investigation. We know, as he justly observes. that nervous matter is formed from our food, which does not contain a trace of it; and there is no absurdity in supposing that an organic compound of appropriate composition, may exert an influence of one kind or other on its formation. Another very important section treats of the nature of the vital force, of that power which regulates all the operations of the body, and which impresses on them their peculiar character. The Professor first points out those particulars in which the vital force, in its manifestations, agrees with other causes of motion or change. He shows that although we cannot hope ever to know what vitality is in its essence, yet it is in our power to trace the laws by which its action is regulated. These laws ingenious dissertation he traces many anaforces of gravitation, cohesion, chemical logies between the vital force and the attraction, and electricity. He arrives ultimately at the conclusion, that the vital force is a force sui generis, in some respects analogous to, yet distinct from all the forces just enumerated. in vain to penetrate the veil that conceals We endeavour the mystery of life from our sight; but in tracing, as far as we are permitted to do so, the causes of motion in the animal body, we come ultimately to chemical attraction, modified in a very remarkable manner by the unknown force. We have seen that chemical attraction explains the change or waste of matter, and the animal heat; and we may add here, that the nervous influence appears to depend, in some way, on chemical changes in the substance of the brain. It is certain, at least, that the exercise of the functions of the brain is attended by waste of its substance, just as the use of the muscles is attended by waste of their substance. Mr. Liebig regards the nerves as conductors of the vital force, by means of which an equilibrium of force may be established; or available vital force may be conveyed from one part where it is not wanted, to another where it is rapidly consumed in producing motion. As the involuntary muscles never cease their motions, sleep is necessary that the waste in the voluntary as well as involuntary muscles may be supplied. In the waking state, one voluntary muscle may be acquiring new matter, while another which is exercised is undergoing waste. In pursuing this investigation, we find that the waste of matter, the supply of oxygen, and the amount of force, mechanical or otherwise, exerted in the body, are most closely connected together. In plants for want of nerves, the vital force cannot be conducted away from the point where it is produced; it therefore manifests itself in an unlimited growth or increase of mass. In animals the presence of nerves permits the vital force to assume at one time the form of chemical attraction, at another that of mechanical force; and when the nerves lose, wholly or partially, their conducting power, we have paralysis, syncope, or spasm. But we feel the impossibility of giving anything like an accurate notion of this most interesting section, unless were to quote the whole of it. Recommending it, therefore, to the physiologist, we shall merely transcribe the concluding paragraph. we 'In what form, or in what way, the vital |