SUMMARY. 119 



The proportion of lysine is likewise small, especially compared with that 

 obtained from the leguminous seeds. The amount of histidine, however, 

 does not differ very greatly from that of the other seed proteins. What 

 significance these differences have in respect to the nutritive value of these 

 different proteins must be determined by future investigation, for it has only 

 very recently been discovered that such differences exist. 



That a molecule of gliadin can have the same nutritive value as one of 

 casein would seem impossible if one molecule of food protein is transformed 

 into one of tissue protein, for in the former lysine is wholly lacking, and 

 glutaminic acid, ammonia, and proline are in great excess over the amount 

 required to form any of the tissue proteins of which we know. It would 

 seem probable that either the animal requires a variety of food, so that the 

 relative proportion in which the amino-acids are available for its use shall 

 correspond more nearly to its requirements, or that only a small part of 

 these amino-acids are converted into its tissue proteins and the rest oxidized 

 as such. It is possible that feeding experiments with proteins of known 

 character in respect to the relative proportions of their decomposition prod- 

 ucts will throw light on these important questions. 



