THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 129 
ot non-nitrogenous nutrients it is still true that the proteid meta- 
bolism, or more exactly the excretion of nitrogen, is mainly deter- 
mined by the supply of it in the food just as it is upon an exclusive 
proteid diet. Fat or carbohydrates simply produce a relatively 
small, and probably more or less transitory, diminution of it with- 
out affecting the substantial truth of the above statement. 
Lawes & Gilbert,* in discussing the results of their fattening 
experiments upon sheep and pigs, called attention to the very wide 
variations in the amount of protein consumed, both per unit of 
weight and especially per unit of gain, and concluded that the ap- 
parent excess of protein in some cases must have served substan- 
tially for respiratory purposes. The subsequent investigations of 
Bischoff, Voit, and v. Pettenkofer upon the proteid metabolism of 
carnivora showed clearly that the dependence of the latter upon 
the proteid supply, which is so marked upon a purely proteid diet, 
is equally evident upon a mixed diet, and thus supplied a scientific 
explanation of the facts observed by Lawes & Gilbert. The 
effect. of the proteid supply upon the nitrogen excretion is clearly 
shown by the following summary of Voit’s experiments: { 
Food. 
Urea Excreted, 
Grms. 
Fat. Lean Meat, 
Grms. Grms. 
250 150 17.0 
300 176 18.9 
250 250 19.7 
200 500 36.6 
200 800 56.7 
250 1500 100.7 
Since Voit’s researches, very many experiments, among the 
earliest of which were those of Henneberg & Stohmann { upon 
cattle, have confirmed his results, both for carnivora, herbivora 
and omnivora. A somewhat striking example is afforded by Stoh- 
mann’s § experiments upon milch goats which are summarized in 
the following table: 
* Rep. Brit Asso. Adv. Sci., 1852; Rothamsted Memoirs, Vol. IT. 
ft Zeit. f. Biol , 5, 329. 
{ Beitriige, etc., Heft 2, p 412. 
§ Biologische Studien, 121. 
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