METABOLISM AND FOOD 67 



these micro-organisms, with the assistance of the 

 nitrogen-free substances, form proteins in one part 

 of the intestines, which are again digested in another 

 part. On the other hand, it is possible that when 

 the bacteria can get such an acceptable food as 

 asparagine or ammonia they destroy less protein, 

 and so leave more available for the real enzyme 

 digestion (p. 22). In this way more protein 

 would be placed indirectly at the disposal of the 

 animal. Bacteria are present in large quantities 

 in the partly digested food of ruminants, whereas 

 considerably fewer are found in that of carnivorous 

 animals. This would explain how the former class 

 are able to make better use of the non-protein 

 nitrogenous substances. 



It has not yet been clearly shown whether other 

 substances besides asparagine and ammonia can 

 act similarly ; for the present it is only possible to 

 say that amido compounds can be utilised by 

 ruminants in the way described. 



For the non-protein compounds in molasses it 

 has been proved that they are not in a position to 

 maintain ruminants in a position of protein equili- 

 brium, to say nothing of causing an increase of protein 

 tissue. Experiments have also shown that the non- 

 protein nitrogen substances of potatoes and mangels 

 are as valueless for the nourishment of rabbits as 

 asparagine is for flesh-eating animals. The pro- 

 ducts which arise on boiling protein with strong 



