BIONOMICS 223 



their food also requires at least some (physiologically) whole- 

 some activity, which may aid the digestion of the carbo- 

 hydrate products of protein metabolism. 



That carnivora rarely survive in captivity may be due to 

 the fact that there, owing to lack of exertion, the bad effects 

 of a too exclusively nitrogenous fare become quickly apparent 

 and cannot be sufficiently met by the powers of digestion, by 

 sufficient oxidation and subsequent elimination. 



It is all, however, a matter of symbiogenetic adequacy; 

 what is wanted is neither too much nor too little 

 heat, and though we shall agree with Spencer in 

 giving to nitrogenous food a less exclusive position than 

 accorded to it by Liebig, for our criterion of adequacy 

 we shall not be guided by such exclusively mechanical 

 considerations as guided both Liebig and Spencer, and 

 some of our modern investigators. What antithesis exists 

 between nitrogenous and non-nitrogenous matter for physio- 

 logical purposes must in many cases be utilised in the same 

 way as we saw the milder kinds of antagonism utilised in 

 Nature, i.e., to produce symbiotic and not antibiotic results. 

 It is not nitrogen per se, nor carbohydrate per se, nor oxygen 

 per se, nor heat per se that is wanted, but their due proportion 

 to perform in the most efficient manner the work of the world. 



Spencer rightly perceives that substances in course of 

 digestion may liberate not only heat, but also other kinds of 

 force ; but I would ask whether these are physiological or 

 pathological symbiotic or antibiotic. He is also correct in 

 saying that this metamorphosis of substances during digestion 

 depends in great part on the conditions ; and they in turn 

 depend, as we have seen, on the conditions of domestic and 

 biological symbiosis. 



The most modern view is that the metabolism of proteids 

 cannot be separated from that of fats and carbohydrates, and 

 that owing to the action of special ferments, not only can 

 sugars be formed from proteins, but occasionally also proteins 

 from sugars (Abderhalden, Dakin, Cramer). Tissue can thus, 



