GENERAL METABOLISM. 



653 



is eaten, and are affected solely by the nutriment which they receive from 

 the circulation, and which has already been assimilated, then we can formu- 

 late the whole question regarding the value of animal or vegetable food in 

 such a way that we shall have to know merely which of the two contains 

 the building-stones of protein in the proportions corresponding more closely 

 to the albumins of the body. As regards the assimilation of the albumin- 

 ous substances in the animal organism, the first thing to consider is whether 

 the protein introduced can be decomposed into its constituents by means 

 of the ferments contained in the intestine, and then whether these build- 

 ing-stones are present in the right proportions. If we examine the pro- 

 teins contained in vegetable and animal food from this point of view, we 

 shall find that the latter correspond more closely to the composition of the 

 protein contained in our own tissues. This is shown particularly plainly 

 in the case of glutamic acid, as is shown by the values given in the follow- 

 ing table: l 



One hundred grams of the protein contain of glutamic acid in grams : 



Unquestionably our present knowledge indicates that the albumin from 

 vegetable foods gives rise to more waste products in the intestine than that 

 from flesh foods. On the other hand, it is perfectly conceivable that a mix- 

 ture of animal and vegetable proteins would enable the animal organism 

 to utilize certain constituents of the latter in common with the former 

 which might otherwise be worthless perhaps on account of a deficiency in 

 glutamic acid. This is, at present, merely a suggestion. It is well, how- 

 ever, to consider such questions from all possible points of view. 



The fact that vegetarians are often under-nourished is worthy of men- 

 tion. They are then obliged to draw upon their own albumin, and live, 

 so to speak, upon animal protein. They are then false to their own 

 doctrine! 



In order to determine the nutritive value of a foodstuff, we must in the 

 first place know its composition. In the following table the composition of 

 one of the most important foods is given. In infancy milk is the chief, if 

 not the only, form of nourishment. We have already discussed the compo- 

 sition of its ash, and have found that it is characteristic of the milk of every 



' Cf. Lecture IX, p. 172 et seq. t and T. B. Osborne and R. D. Gilbert: Am. J. Physiol. 

 15, 303 (1906). 



