34 APPLIED PHYSIOLOGY 



integration entails work upon the excretory organs. In 

 other words, the ideal they would have us aim at is the 

 utilization of protein if that be possible for repair 

 purposes alone. 



Of the stages in the breaking-down of the repair- 

 protein we know very little, but there is reason to 

 believe that, like the preparation of food-protein for 

 assimilation, it consists in resolution by successive stages 

 into amido - acids. In normal circumstances these 

 undergo further destruction, and mere traces of them 

 appear in the urine, but in pathological states they may 

 be excreted in large amounts. The appearance of leucin 

 and tyrosin in acute yellow atrophy of the liver, and 

 the anomalies of metabolism which result in cystinuria 

 and alkaptonuria, are examples of such imperfect 

 destruction. 



2. Fats. 



The assimilation of fat appears to be a much simpler 

 process than that of protein. The fat molecules of the 

 food, having been split up by digestion into fatty acids 

 and glycerine, are absorbed in that form by the cells of the 

 intestine, and apparently immediately reconstituted into 

 fat ; they then reach the general circulation by means of 

 the lymphatics. By the cells fat appears to be received 

 much more as a foreign body than protein is, and there 

 is not the same attempt to recast it into a substance 

 of uniform chemical composition. Hence it is that the 

 fat stored up may partake very largely of the chemical 

 characters of the fat absorbed. If, for instance, a fat 

 of low melting-point be given in large quantities, the fat 

 stored up is apt to be soft. This is, no doubt, the physio- 



