of the Fat of the Animal Body, 441 



the whole of that estimated to be required for the mere suste- 

 nance of the animal (according to its weight) independently of 

 gain or loss, or milk produced. 



It is obvious, however, as pointed out by Voit, and as after- 

 wards admitted by H. von Liebig, that if nitrogenous substance 

 may break up into urea and fat (with other products), the amount 

 estimated to be required for the mere sustenance of the body 

 should not be considered inadmissible for the formation of fat 

 as one of its products, and therefore should not be deducted 

 (with that appropriated for the production of increase and of the 

 caseine of the milk) from the amount supplied in the food in 

 estimating whether or not it provided sufficient for the formation 

 of the fat known or calculated to be produced. 



H. von Liebig states that he selected experiments with cows as 

 the basis of his illustrations, considering that, when in a normal 

 state, the change in the solid substance of the body of the animal 

 was comparatively small, if not indeed immaterial, and that the 

 fixed products of the food, beyond what might be required for 

 the mere maintenance of the body, were accumulated and easily 

 estimated in the milk collected ; whilst he considered, on the 

 other hand, that the point in question could not be settled by 

 reference to results relating to fattening animals, without the aid 

 of an apparatus for the determination of the products of respiration 

 and perspiration. We believe, however, that with a proper selec- 

 tion of fattening animals it may be satisfactorily illustrated 

 without the aid of any such apparatus ; and it is the object of 

 this paper briefly to discuss the question of the sources of the 

 fat of the animal body by reference to the results of experiments 

 with such animals. 



As already intimated, the objections of Dr. Hayden to the 

 supposition that fat is formed from the carbo-hydrates of the food, 

 were based upon physiological considerations of a qualitative, but 

 not at all of a quantitative kind. Voit's argument was, on the 

 other hand, founded upon strictly quantitative results, obtained, 

 however, under conditions as to choice of animal and of food, in 

 which the formation of fat, if it took place at all, must of ne- 

 cessity be attributed to the nitrogenous constituents consumed. 

 H. von Liebig also relied upon quantitative results as the basis of 

 his illustrations ; but those selected, when properly considered, 

 afforded, to say the most, only negative evidence on the point. 



The question arises — What description of animal is the most 

 likely to yield the most direct and conclusive evidence as to the 

 source of the fat stored up in its body ? Obviously the one" 

 which is fed more especially with a view to the production of 

 fat, which consumes in its most appropriate fattening food a re- 

 latively large proportion of carbo-hydrates, and which yields a 



