64 THE AMINO ACIDS 



perhaps by each individual cell. Although the tissues 

 all probably possess this power of breaking down pro- 

 tein material by means of their intracellular proteolytic 

 enzymes, still the extra work involved seems to nega- 

 tive the immediate resynthesis hypothesis, especially 

 when the hypothesis of the circulating digestion pro- 

 duct postulates the presence of the individual food 

 material in the blood. As already remarked, the mere 

 failure to detect these products in the blood does not 

 give adequate reason for concluding that they are not 

 present. The tissues certainly do not break down in 

 regular sequence, nor are they left to fall to pieces for 

 lack of repair material. Repair is among the most 

 active functions of all tissues. Must, then, a tissue 

 of highly complex structure keep destroying and digest- 

 ing plasma, picking out from the debris the nuclei 

 which it requires and letting the rest go ? (Why, and 

 this destruction is admitted by Abderhalden, are the 

 superfluous amino acids not found in the blood?) 

 What happens, for instance, in the case of connective 

 tissues with their demand for, say, glycine, where the 

 food supply is not over-abundant as the circulation is 

 poor, and the tissues not very suited for lymph per- 

 fusion? It will not do merely to say that there is no 

 great breakdown of material here. Pfliiger, in an inter- 

 esting paper in which he combated this immediate 

 resynthesis hypothesis, ascribed to the cells of the 

 intestinal wall, with regard to the protein synthesis, 

 the same capacity as the cells of all tissues, but denied 

 that the synthesis of protein for the whole organism 



