NUTRITION in 



The two theories are not necessarily irreconcilable, and, 

 in the author's opinion, it is difficult to resist the conclusion 

 that to a certain extent both are correct, i.e. that some of the 

 food material is directly oxidised in the blood, and that 

 some is used to repair the waste due to oxidation of the 

 tissues. 



So far as repair of the waste or formation of new tissue 

 is concerned, it is at once obvious that nitrogenous matter 

 (protein) cannot be formed from non-nitrogenous matter (fat 

 and carbohydrates). It is essential, therefore, that an amount 

 of nitrogenous matter adequate for these purposes should be 

 supplied in the food. This conclusion is amply borne out 

 by numerous experiments. If the supply of protein in the 

 food is insufficient, the animal dies of nitrogen starvation. 



It has further been shown that the protein must be of the 

 right kind. Gelatine, for example, will not do. It tends 

 to minimise the waste, but by itself it cannot wholly repair 

 it. Gelatine contains no tyrosine, tryptophane, or cystin 

 (p. 52), and is probably lacking also in other radicles that 

 are essential for the formation of the complex proteins of which 

 the animal's body is built up. Indeed there is some reason 

 to believe that any one of the vegetable proteins is not 

 by itself adequate for the purpose. It was found that mice 

 died of nitrogen starvation when zein (p. 74) was the only 

 nitrogenous constituent of the food. The proteins of any food 

 are rarely, if ever, all of one kind, but often one predominates. 

 If the proteins, are derived from several kinds of food, the 

 chances are increased that the products into which they are 

 resolved by the processes of digestion will furnish all the 

 constituents required. These constituents can then be selected 

 in the proportions required ; if any one or portion of one is 

 not utilised in this way, it will, of course, pass into the 

 blood and be further oxidised. This is one reason there 

 are others why the food should be of a mixed and varied 

 character. 



The question then arises whether the non-protein nitro- 

 genous compounds (amides) are of any value for the nutrition 

 of animals. On this point the opinions of authorities are 



