The slight difference between the figures obtained by these different manners of calculation, points to the correctness of the methods.

The loss of the dog during twenty-four hours, estimating its medium weight to be 31.8 kilogrms., was for one kilogrm. 0·30 grm. nitrogen, and 5.67 grms. carbon.

The warmth developed by the animal during twenty-four hours was computed from the carbon and hydrogen of the consumed tissue, a portion of the hydrogen (20-7 grms.) corresponding to the oxygen present in the same tissue (166-1 grms.) having been previously abstracted, as not contributing to the development of warmth. For the remainder of the carbon (1075.7 grms.), and hydrogen (124-06 grms.), the authors have adopted the figures of Favre and Silbermann-viz., for 1 grm. carbon 8086 units of warmth, and for 1 grm. hydrogen 34,462 units of warmth. According to this computation, the animal developed 12,976,466 units of warmth during the six days of the experiment; therefore during twenty-four hours, 2,162,744 units of warmth.

Bischoff and Voit are, however, aware that this method of calculation gives, at the utmost, only an approximative result; that it is doubtful whether the heat-creating power of fat, sugar, and similar substances, depends strictly on their per-centage of carbon and hydrogen, and whether the oxygen contained in combustible substances is to be considered as already combined with part of the hydrogen in the proportion of water. The heat-equivalents for carbon and hydrogen appear, besides, to be not yet ascertained with perfect certainty; those adopted by Liebig, for instance, in his twenty-eighth letter, are for carbon 7881, and for hydrogen 33,808 units; therefore perceptibly smaller than those of Favre and Silbermann.

The results of the authors' various observations on the phenomena of nutrition in starvation, do not materially differ from those of other observers; they show the minimum amount of tissue-metamorphosis under given circumstances; they prove that, the other influences remaining the same, the consumption of tissue is in exact proportion to the condition of the animal; that with the decrease of the weight of the latter, the quantity of tissue undergoing decomposition, decreases likewise; that this law is true, not only with regard to the entire animal, but also with regard to the single constituents of its body; that, for instance, a starving animal, which is relatively rich in fat, consumes a larger proportion of fat, one relatively rich in flesh more flesh. The latter phenomenon the authors explain, by supposing that the bulk of nitrogenous tissue being relatively great, a larger quantity of its substance undergoes a change of combination of molecules; that thus a larger amount of primary products of nitrogenous tissue-change is formed, which in their further oxidation occupy relatively much oxygen, leaving only a small quantity available for the oxidation of fat. The fact, on the other side, that a fat animal, when starving, de

composes relatively little flesh and much fat, is interpreted by the assumption, that the greater bulk of fat appropriates more oxygen, and thus diminishes its action on the flesh.

This interpretation may be correct, but others might have the same claim. Thus, for instance, in an animal comparatively rich in fat and poor in muscular tissue, the phenomena of innervation—and this we consider a point of great importance may be considered to be less active, the quantity of nutritive fluids may also be conceived to be smaller, and proportionally to this, the amount of activity connected. with their locomotion; the nitrogenous tissue-change under such circumstances would be less active, and as a consequence of this the consumption of fat would be relatively great; while, according to Bischoff and Voit, the presence of the greater bulk of fat would be the primary cause of its greater consumption, and the diminished waste of nitrogenous tissue its consequence. In an animal rich in nitrogenous tissue, on the contrary, the phenomena of innervation might be deemed more active, and also the quantity of nutritive fluids greater, requiring more activity in their locomotion; through all this, and not merely through the large bulk of nitrogenous organs, a comparatively considerable nitrogenous tissue-change may be effected.

The authors' calculations on the production of heat during starvation are important, as their inferences regarding the consumption of tissue in other series of observations are to some degree based on them. According to these calculations, the minimum of heat developed by the dog in question during twenty-four hours amounts to 2,200,000 units.

II. On the metamorphosis of tissue during flesh-feeding (pp. 56-97), the authors offer fourteen tables.-The flesh used was "good fresh cow's flesh; fat, bone, cartilage, and other admixtures, were always carefully removed." It seems that only some specimens of the flesh used have been submitted to analysis, and that these contained, at an average, scarcely one per cent. of fat. Considering the very great degree of care bestowed on these experiments, it would have appeared more satisfactory, if specimens of all the flesh used had been analysed, at least with regard to the per-centage of fat, salts, and water; but the manner in which the results of the various experiments agree amongst themselves, permits us to consider them as trustworthy, in spite of the slight deficiency mentioned.

A similar, though unavoidable inaccuracy presents itself with regard to the fæcal excretions. Their analysis has been performed only in an approximative manner; and, besides this, the animal's evacuations having been passed sometimes at long and uncertain intervals, the authors were often obliged to apportion, by calculation, certain quantities to former series of observations.

The fourteen series of observations on pure flesh-feeding exhibit great variety, not only with regard to the quantity of flesh fed, but also with regard to the state of the animal's nutrition at the beginning of each series. Every single series offers points of great interest; we will, however, mention only the results of the eleventh more in detail.

The dog, after having been fed during several days merely on broth and bread, weighed at the commencement of the experiment 32,990 grms. The animal then took, on three successive days, 2000 grms. of flesh daily, therefore 6000 grms. in all. It lost during this period, the fæces having been accounted for, 89 grms. in weight.

"What did this loss consist in? The 6000 grms. flesh contained 204 grms. nitrogen. The dog excreted 380-86 grms. urea, with 177.75 grms. nitrogen; the 94 grms. fæces contained 28:56 grms. solids and 65 44 grms. water, and in the former 1.86 grm. nitrogen. The dog excreted, therefore, in all, 179 61 grms. nitrogen, or 24.39 grms. less than it had received in the flesh. These correspond to 717 grms. flesh, which, therefore, the animal had appropriated. As, however, notwithstanding this, it lost 89 grms., it must have yielded 806 grms. of water or fat." (p. 86.)

"During twenty-four hours the animal excreted:

This gives for 1 kilogrm. dog during twenty-four hours, the average weight being 32.76 kilogrms., 1.83 grms. nitrogen and 6.73 grms. carbon.

With regard to the production of warmth, 166 85 oxygen require 20.86 hydrogen. The combustion of the remaining 43-33 hydrogen, and 572-86 carbon, yields 6,125,384 units of heat, and for twenty-four hours 2,041,795 units." (p. 87.)

As the minimum of warmth for twenty-four hours amounts to 2,200,000 units, there is for every day a deficit of 158,205 units, corresponding to about 16 grms. fat which the animal consumed from its own body; the dog lived, therefore, during the three days, on 5283 grms. flesh, about 48 grms. fat, and 1238 grms. water (viz., 758 from its body, and 480 grms. taken during the experiment).

This observation proves, according to our authors, that the amount of nitrogenous tissue-change depends, to a great degree, on the condition of the animal, and especially on the bulk of the nitrogenous organs. In the present instance the animal appropriated, during three days, 717 grms. of nitrogenous substance out of 6000 grms. ingested during that period; while in another experiment, 4000 grms. which the animal took within two days, were not sufficient to repair the loss sustained during the same period by the metamorphosis of tissue. In the latter case the animal, just before the experiment, had received 2500 grms. flesh daily, while it had been fed on broth and bread previously to the series under consideration. The nitrogenous tissue of the animal, after the flesh-feeding, may be assumed to have been in good condition, while during the bread and broth diet a part of it had, we may suppose, been wasted and supplanted by water. This supposition is rendered still more probable by the fact, that during the experiment just detailed, the dog lost water and appropriated nitrogenous tissue.

This observation teaches us also, that the weight alone cannot always entitle us to form conclusions regarding the state of an animal's nutrition, for in spite of the considerable gain in nitrogenous substance,

and the only small loss of fat, the dog's weight had decreased through the loss of water. It was by basing his calculations on the weight alone, that Bischoff in his former essay, 'On the Urea as a Measure of the Metamorphosis of Tissue,' was led to maintain, that not all the nitrogen is eliminated by the kidneys, but that about one-third of it escapes in some other way than as a component of urea. It is, however, quite clear that a dog fed on two pounds of flesh may exactly keep his weight, not only by transforming these two pounds into tissue and losing two by decomposition of tissue, but also by consuming through the tissue-change a pound and a half of flesh and half a pound of fat, or two pounds and a half of flesh, and retaining half a pound of water. Bischoff himself explains his former error, and believes now, with his joint author, that, by a fundamental law, all the nitrogen in the dog, with insignificant exceptions, is excreted through the kidneys as urea. It will be remembered, that in this respect Bischoff and Voit are in harmony with Bidder and Schmidt, who have established the law in question, with regard to carnivorous animals in general, in their well-known treatise On the Digestive Fluids and the Metamorphosis of Tissue.'

Amongst the results from the experiments on flesh-feeding alone, we further remark, that the dog can be maintained in good condition by flesh alone, without losing either flesh or fat; that this, however, requires an amount of flesh equal to one-twentieth to one-twenty-fifth of the entire weight of body. This experience is rather opposed to the view of Liebig, who thinks it "exceedingly doubtful whether these substances, considering their properties, would, in the circumstances under which they are presented to oxygen in the organism, produce the necessary temperature of the body, and compensate for the loss of heat, for of all organic compounds, the plastic constituents of food are those which possess in the lowest degree the properties of combustibility and of developing heat by their oxidation."

"Of all the elements of the animal body, nitrogen has the feeblest attraction for oxygen; and what is still more remarkable, it deprives all combustible elements, with which it combines to a greater or less extent, of the power of combining with oxygen-that is, of undergoing combustion."'

It might be said, in support of Liebig's view, that flesh is never altogether free from fat and non-nitrogenous elements, yet, if we may accept the authors' assertion, that the flesh supplied by them to the dog contained rather less than one per cent. of fat, their inference would not be materially restricted owing to the presence of so small a proportion. From the experiments on mixed flesh and fat feeding, it appears, at all events, to result, in opposition to the second remark of Liebig's, that, within the animal body, the oxygen has as great, and even a greater affinity to the primary products of metamorphosis of the nitrogenous tissues (not to the unchanged tissues themselves) than to fut.

Bischoff and Voit further infer, that if the flesh offered to the dog • Liebig's Familiar Letters on Chemistry. Fourth edition, edited by John Blyth, M.D.' p. 39 4. London, 1859.

is less than one-twentieth to one-twenty-fifth of its entire weight, it consumes in addition a part of the nitrogenous and fat-tissues of its body.

If the dog receives more than is necessary for the repair of its tissue, it appropriates the surplus. As soon as, through this, the animal's weight has become increased, a proportionally larger amount of food is required to repair the necessary tissue consumption, and a still larger one in order to ensure further increase. If the latter is offered in an increasing proportion, the dog arrives at last at a maximum weight; it then ceases to take food, and consequently, the metamorphosis of tissue being uninterrupted, rapidly loses weight, until it again acquires the power of taking food.

The quantity of flesh necessary to repair the loss effected by the tissuechange, or to cause increase of flesh, depends on the amount of nitrogenous tissue in the body, the animal possessed of relatively much flesh requiring more than that poor in flesh.

The amount of nitrogenous tissue-change becomes increased by the ingestion of nitrogenous food, and in proportion to the amount of the latter. If the animal receives only the quantity corresponding to the tissue-change during starvation, it continues to lose weight, because the amount of labour to be performed is augmented, and consequently the decomposition of tissue increased, through the ingestion of food and the larger amount of blastema thus produced. The decomposition of nitrogenous tissue would in this manner, the authors maintain, always go on increasing with the increase of ingestion; the animal would perish from starvation, in spite of the increased amount of food, if not, the quantity of oxygen available being limited, at last the point would be reached when the whole of the oxygen would be occupied by the primary products of the metamorphosis of the nitrogenous tissue for their further oxidation. It is only then that the animal ceases to lose, and that if a further addition is made to the food, it begins to gain weight. By the progressing increase of ingestion the weight of the animal may then be progressively raised unto that limit, when, as already mentioned, and as shown by Table XII., on flesh-feeding, the animal becomes unable to take food for a time, until a certain amount of retrogressive tissue-change has taken place.

These experiences, and the relation of the excretion of urea to the ingestion of various quantities and qualities of food, and to the tissuechange during starvation, lead the authors repeatedly to discuss the question of the source of urea, and the theory of the so-called "luxusconsumption," that theory which teaches that, whenever more albumen is introduced into the system than is necessary for the repair of the nitrogenous tissue-change, this superfluous albumen is at once oxidized within the blood, without having previously entered into the formation of tissues, and that this immediate decomposition of albuminous substances is the cause of the rapid increase of urea after large meals (Lehmann, Frerichs, Bidder and Schmidt). Bischoff and Voit hold this theory as entirely unfounded, and maintain with Berzelius, Müller, and Liebig, that it is impossible that urea can be formed rom albumen in any other way than by the decomposition of the