INFLUENCE OF THE FOOD ON THE TISSUES 65 



change which takes place in the salmon during the development of the 

 genitalia is a mere change of position rather than the result of syn- 

 thetic action. Noel Paton (318) has shown that the amount of fat 

 which the salmon accumulated in its muscles during its sojourn in the 

 salt water is not only amply sufficient to yield all the fat required by 

 the growing sexual glands, but is also sufficient to yield the energy for 

 an enormous amount of muscular work. In this way the protein of 

 the muscle tissue apart from the ordinary wear and tear, is not called 

 on to supply the energy required for movement. It must also be re- 

 membered that the salmon starts from the estuary for its ascent of the 

 river with a very large store of some soluble protein in its tissues, and 

 that this steadily diminishes in amount (Boyd (72)). Is this soluble 

 protein a highly specialized one eminently suited for the formation 

 of protamine or is it ordinary protein filling out the cells and which is 

 used either for energy or building purposes? 



On the other hand, the evidence adduced by Henriques and Han- 

 sen (187, 1 88) in connexion with an entirely different question must 

 not be forgotten. These workers stated that they were able to get 

 rats into a state of nitrogenous equilibrium when they fed them solely 

 on the monamino acid fraction of a digest. Now if these experiments 

 be accepted many workers, as already mentioned, doubt the accuracy 

 of metabolic experiments carried out on rats then we must at the 

 same time accept the synthesis in the organism of the diamino acids, 

 not to speak of other complex nitrogenous bodies precipitated by the 

 phosphotungstic acid, from simple amino acids and simple polypeptides. 



Again, the experiments which have been carried out where aspara- 

 gine has formed the sole source of the nitrogen supply (see Chap. III., 

 section 2) synthesis not only of the diamino, but also of the other 

 monamino acids, aliphatic, aromatic and heterocyclic. It may be that 

 in these experiments the bacteria alter the asparagine before absorption 

 takes place. 



And finally the growth of moulds like Aspergillus Niger on a 

 medium containing potassium nitrate or glycine (12) as the sole source 

 of nitrogen is evidence of the synthesis of amino acids, for a protein of 

 complex structure is formed from which glycine, alanine, leucine, 

 glutamic and aspartic acids can be isolated. 



