clude the comparative anatomy of reptiles, birds, and fishes; and we trust that Professor Owen may not be driven, by the numerous demands upon his time and attention, to that system of indefinite postponement, which has manifested itself of late in the delay of the later portions of almost every anatomical work that has been published in detached parts or volumes. Having ventured upon something like a promise as to the time of its appearance, we hope that he will not indulge the belief that literary "promises, like pie-crust, are made to be broken."

ART. XIII.

1. Animal Chemistry; or Chemistry in its Applications to Physiology and Pathology. By Baron LIEBIG.-London, 1846.

Svo.

2. Experimental Researches on the Food of Animals and the Fattening of Cattle; with Remarks on the Food of Man. By ROBERT DUNDAS THOMSON, M.D.-London, 1846. 8vo.

THE minute study of the nature and relations of the food of animals and plants has often appeared to us calculated to elucidate, not only the practical points, which are at once obvious even to a superficial observer, but also to throw a light upon several more abstract physiological questions, which have been debated too often with a reference merely to one phase in the history of organized beings. In directing our attention to some of the new views which have been broached upon the nature of food, it may not be out of place briefly to consider the bearing of the subject upon one or two of these disputed points.

A proper distinction between the animal and vegetable world has long been a desideratum with the physiologist. Nor will the circumstance of the question being still undecided appear remarkable, if we reflect that correct notions are scarcely yet formed of the proper constituents of the frames of the two classes of beings, and more particularly that the source of these substances is still disputed. But scientific men have even experienced much difficulty in defining the general characters of vegetables and animals. The former being confined to one spot, and the latter being moveable, some have considered that animals were distinctively locomotive. But it so happens that many of the lower tribes of animals are incapable of locomotion, and hence this definition is untenable. Others, observing that plants are destitute of sensation, have proposed to ascribe this attribute alone to animals, and define them as nervous beings. But in opposition to this view, we find many inferior animals apparently destitute of sensation, and only supplied with a degree of irritability even inferior to that of the sensitive plant, cultivated so frequently in our botanic gardens; and hence this definition also fails us. We believe that the true distinction between animals and vegetables will be detected more readily by discovering the nature of the matter by means of which they increase in bulk, or, in other words, by the nature of their food-the term food being a word applied to express the matter which enables plants and young animals to increase in size, and full-grown animals to preserve their forms unimpaired. According to this view then, it is from chemical physiology

that we are to expect an answer to the questions, "What is an animal?" "What is a vegetable?" To one accustomed to view only the larger kinds of animated beings it might seem an easy task to give a reply to these questions. But when we know that nature is simple in her works; that in her we find no sudden leaps from great to small, but that the whole animated world consists of a chain formed of a series of beings passing down in regular gradation from comparatively the most perfect to the most imperfect state, the lowest plant being closely allied to the lowest form of animal, it will at once be obvious that to say where plants begin and animals end cannot be a problem of easy solution.

To apply, however, the test which we have proposed, let us begin with plants. We find a plant cultivated among the Chinese and introduced among ourselves, termed the air-plant, which, by being merely suspended in the air, increases in bulk and weight without even the application of water. This is one of the most simple forms of vegetable life, as the plant has nothing to feed on save the atmosphere, which, however, contains all the elements necessary for its growth-oxygen, vapour of water, carbonic acid, and ammonia or some form of nitrogen. But all these are gaseous bodies or vapours, while the air-plant is a solid; hence we infer that this plant is capable of reducing gases to the solid form, and of thus increasing in bulk and weight. According to the views of persons best qualified to judge, it appears that all plants are endowed with similar properties, and that they mainly subsist by feeding on the gases which surround them, by converting these gases, by means of the organs with which they are supplied, into the solid forms of the vegetable kingdom, so endless in figure, but yet so lovely, that the greatest familiarity only renders them objects of superior admiration.

When we turn to the animal world, we find that the individuals of which it is composed are incapable of condensing gases; in fact the least educated knows that animals derive no sustenance from air; but that they require to imbibe solid matter similar to that of which they consist. Man lives upon animal food, and those kinds of grain which contain matter nearly allied to it. The question, why has grass, perhaps the most abundant vegetable in nature, never constituted a portion of human food, unless perhaps among the most degraded of the species, may not strike us as being in its answer fraught with important information. And yet the only reason which can be given for the fact, that it has never been an article of human food, is, because it contains such a small portion of matter similar in its nature to the constituents of man's frame, that the quantity required would be too voluminous for the digestive capacity of the stomach and other organs. An animal may therefore be defined, according to this view, to be a being which subsists by appropriating to itself food similar to the matter of which its own body is composed. Hence we see the necessity for its locomotion; while a plant, finding its nourishment in the air which constantly surrounds it, has its food brought to it by the usual laws of inanimate nature. We believe, then, that such will be found the most correct mode of separating animals from plants. It is probable that among the inferior tribes of animals, where an approximation is made to the vegetable kingdom, there may be individuals partaking of a semi-vegetable and animal nature, partly living on air and partly on solids. Although it does

not follow that such an occurrence is necessary, yet, from the simplicity and gradation which we find subsisting throughout nature, we might expect to discover some such union of the two kingdoms, or some equally simple transition from one set of beings to the other. To discover whether any such series of beings exists, it is obvious that we can proceed upon the principles which we have now been discussing. For example, if we find any usually considered plant or animal possessing in its constitution some substance which we know to be peculiar to a plant, and capable of being produced from gases through the instrumentality of the vegetable organism; and further, if we never find this matter present in animals, we seem to be drawing a legitimate conclusion when we infer that these species partake of a vegetable nature, and that we are approaching a point in creation, where the two great organized kingdoms are closely allied, or insensibly passing into each other.

This investigation has been commenced and has been followed by a successful result in one or two instances. It was observed some years ago by Wöhler, that the frustulia salina of Ehrenberg, a small zoophyte found in the slimy matter of saline springs at Königsborn, disengages large quantities of pure oxygen, so that when the mud containing a number of these beings is stirred with a stick, a beer-glass of water inverted may be filled with the gas in a very short space of time. This remarkable phenomenon, which never occurs in the clearly established animal race, but is a characteristic of plants, naturally attracted the attention of chemists, and, accordingly, upon examination by Schmidt, it was found that the constitution of this zoophyte shows that it is closely allied to the vegetable kingdom. A substance was extracted from it, which, after treatment with ether and dilute caustic potash, gave, by analysis, the silica being subtracted, the following composition:-carbon 46-19, hydrogen 6.63. Now these are exactly the numbers which have been obtained as expressing the composition of the basis of that inferior though familiar class of plants the lichens. The inference then seems legitimate, that the substance which constitutes the walls of the cells of at least this class of plants is identical with, in composition with, a substance found in the frustulia salina. If we compare the constitution of the cells of decided animals with that of vegetables, we find a sufficient distinction in the presence of nitrogen in the animal, and its absence in the vegetable cell. If we distil each of these matters respectively, we obtain an ammoniacal fluid in the one case, and an acetic fluid in the other, a distinction pointed out between animal and vegetable substances so long ago as 1742 by Beccaria of Bologna. (Thomson's Researches on Food, p. 158.) All such chemical results, it is obvious, therefore, are important in enabling us to arrive at a conclusion in reference to the nature of the food of different beings, and therefore of the position which these beings hold in the scale of creation. So important, therefore, is an acquaintance with the nature of the food on which such beings subsist even to the physiologist.

Again, in the cynthia mammillaris, a species of ascidia, there is a thick fleshy sack connected with the gills, liver, &c., which consists of a congeries of large cells similar to the parenchyma of the cacti and many fruits. Upon its inner side numerous vessels expand, which communicate with the gills. When this outer sack is successively treated with water, alcohol,

ether, dilute acids, and alkalies, a colourless membrane remains, which is not altered by nitric, hydrochloric, acetic acids, nor by the most concentrated solution of caustic potash. It is quite destitute of nitrogen, and when analysed, was found to consist of 45.38 per cent. of carbon, and 6.47 of hydrogen, a composition identical with that of the cellular membrane of plants, which has been termed cellulin or cellulose, and is identical in composition with starch and sugar. In the preparation of the substance as previously described, the solution of potash in a caustic state dissolves up from the cellulin a quantity of azotized matter possessing albuminous properties. So that the cells of the beings examined were quite analogous to those of plants in more than one point of view, as it is an operation of some difficulty to separate the nitrogenous constituents of a plant from the cellular matter in those species on which no doubt exists as to their proper position in the organized scale.

From the observations which have been previously made, it is apparent that before we can point out the proper food destined for animals, we must study carefully their habits and endeavour to discover the food which they prefer when left freely to the enjoyment of their instincts. It is evident that there are certain laws which nature has laid down that serve to guide even the lower animals in the choice of their food. It is a rare occurrence to hear of the suicide or accidental death of a domesticated animal; still less frequent that of a creature which is free to roam amid the wild scenes of nature. We remember one case in which some dried and powdered monkshood (aconitum napellus), to the extent of a quarter of an ounce, was licked up by a pony. The animal suffered considerably, as if under an attack of glanders, for a few hours. But these instances are so rare that it might almost be affirmed that man is the only created being which disobeys the laws of nature; and it is merely when domesticated and under circumstances analogous to those in which man himself is placed, that we find the inferior creation imitating by such experiments their more godlike superiors.

It is of essential importance to decide by what method we are to arrive at the nature of the proper food of animals. There must be no petitio principii. With all our reverence for Scripture, therefore, we must protest against the conclusions which some well-meaning, but one-sided medical commentators have drawn, as to its being employed as a text-book for all or any of the sciences. Its object was moral, not physical, and the statements that occur in it in reference to science of all kinds, are necessarily such as are consonant with the opinions of those who lived in the earliest ages. If they had been, or could have been otherwise, it is highly probable that these writings would never have reached our times; but have long since been consigned to oblivion as the records of physical impossibilities, and of erroneous speculations in science, or as the dreams of the mystics. Nor are we to expect to derive physical truth from the lucubrations of the often well-meaning, but equally ignorant mere humanity-mongers, who "strain out the gnat and swallow the camel," exhibiting in themselves, as with all ultra-advocates, the most distressing instances of human inconsistency. These are imitators of Pythagoras, not only in their support of a so-called humanity, but also in their advocacy of the principle without consistency. That distinguished philosopher could exclaim against the

abominable wickedness that men should permit bowels to be buried in bowels, that one greedy body should grow fat with another body crammed into it, and that one animal should live by the death of another animal, and characterize the use of animal food, as champing with the teeth nothing but dreadful wounds, and thus reviving the manners of the Cyclops. "Why has the sheep deserved death," he asks, with vehemence, “that harmless animal which carries nectar in its full dugs, and furnishes us with soft clothing and aids us more by its life than its death?" At first sight, it is impossible to avoid sympathizing with the energetic and poetical eloquence of such a humane advocate. But the scene is suddenly changed; our sympathies are drawn back to our own bosoms, and another variety of feelings is engendered when we remember that this remarkable philosopher, as if to demonstrate that ultra views necessarily produce inconsistency, gave the lie to all his aspiring sentimentality, by sacrificing in the most cruel manner, and without any ulterior object to serve, 100 oxen in commemoration of his discovery, that the square on the hypothenuse of a right-angledtriangle is equal to the sum of the two squares on the base and perpendicular. So striking is this imperfection in his character, that his apologists suggest, but without any authority, that the oxen must have been composed of wax. But let it not be supposed that such opinions have fled before the light of knowledge, which has been promulgated during the 2344 years that have intervened since his death." For we find the same school of humanity-mongers, at the termination of that long period of time, still inculcating the idea in reference to the use of animal food, that "the man of cultivated moral feelings shrinks from the task of taking the life of the higher grade of animals, and abhors the thought of inflicting pain and shedding blood," just as if this were a correct statement of the question. While we therefore protest against every needless occasion of suffering, to all classes of animated nature, we should characterize such bastard humanity as we have alluded to as beneath consideration, nay in many cases as insufferable, if carried out with any semblance of consistency.

Some of the exclusively vegetable dietists, who base their doctrines upou a kind of one-sided metaphysico-historical research, commence by asking and solving the question as to the original food of man, not by the simple physiological method of observing the nature of the food with which the mother is supplied by nature for the support of the original man, but by speculating respecting the food used in the garden of Eden. The primary and original food of man, whatever speculators may say to the contrary, is milk, a fluid of animal origin. If those who are to regulate diet are not guided by scientific knowledge, and are not to exercise their judgment, they might be inclined to draw from this fact the conclusion that the proper nutriment of man is animal food, and this deduction might be defended with great show of reason to the exclusion of a vegetable diet altogether. But observation having proved that animals can subsist upon a vegetable as well as upon an animal regimen, and scientific research having satisfactorily demonstrated that the constituents of the two kinds of nutriment when well selected are identical, the one-sided position which might have previously been assumed and strenuously maintained, must yield to the lights of knowledge.