328 SCIENTIFIC FEEDING OF ANIMALS 



stances, and that they do not by a long way attain 

 the influence of the protein, even when a sufficient 

 quantity of nitrogen-free material is present in the 

 ration. If the food, as in some investigations was 

 the case, contained more protein than the animals 

 needed, it would be immaterial whether the excess 

 were replaced by non-protein nitrogenous sub- 

 stances or not, for the replacement of proteins 

 by compounds of this nature can only have an 

 influence on the formation of milk when, before 

 the substitution, no excess of protein is present. 

 Investigations on this point have only so far 

 been tried with ammonia, which, combined with 

 acetic acid, was fed to the animals. It was found 

 that ammonia could be as completely utilised for 

 milk formation as are the proteins, provided a 

 sufficiency of nitrogen-free substances was present. 

 It was noticed, though, that thereby more carbo- 

 hydrates were used, which may be explained by 

 assuming that in the formation of proteins from 

 this material other food constituents must be 

 utilised at the same time. In this way the re- 

 placement of 168 g. of digestible protein by an 

 amount of ammonia which had the same quan- 

 tity of nitrogen as the protein was possible, and 

 without, as it proved, any change being made in the 

 percentage composition of the milk. 



There are then nitrogenous substances of a non- 

 protein nature which can, where there is plenty of 



