68 SCIENTIFIC FEEDING OF ANIMALS 



acids have also shown themselves unable to replace 

 food protein when fed with large quantities of 

 nitrogen-free substance to dogs, rats, and mice. 

 Only with those substances which result from the 

 decomposition of protein by pancreatic juice, and 

 which contain therefore all that is in the protein, 

 has the effect on carnivora been shown to be 

 the same as with proteins themselves. Many in- 

 vestigators have prematurely concluded from this 

 that the amides of the food, if fed together and not 

 alone, must give results similar to those from the 

 proteids. That, however, could only be the case 

 if the mixture of amido substances in each food 

 contained the materials from which protein could 

 be built up, as the products of digestion just 

 mentioned do. The above experiments with the 

 amides of potatoes and mangels prove this as- 

 sumption to be incorrect. It will be remembered 

 that even gelatine, which stands in very close 

 relation to protein and is, in fact, put in that class, 

 cannot take the place of the true proteins in the 

 case of carnivorous animals (p. 61). 



Investigations as to the part which non-protein 

 nitrogenous compounds play in the formation of 

 fat have so far only been made with asparagine. 

 Upon sheep it has been shown that these materials 

 cannot be changed into body fat. This agrees per- 

 fectly with the fact that asparagine, where it is not 

 changed by the bacteria of the intestines, possesses 



