30 THE PHYSIOLOGY OF PROTEIN METABOLISM 



generated peptone. They believed that it was a mixture and suggested 

 that " rennin proteose " should be the name given to it. They ob- 

 tained it from the different proteose fractions. Sawjaloff, in a later 

 paper (355), restated his position and again maintained that the forma- 

 tion of plastein was a true synthetic process, and that it could only be 

 demonstrated in strong proteose solutions. He thought that in all 

 probability it was evidence of a reversible action of pepsin. He re- 

 garded it as an assimilation product of first-rate importance, the in- 

 termediate product between digested protein and the formation of 

 blood proteins. This change took place, he believed, immediately 

 after absorption. He was convinced, that when proteins have reached 

 what may be called the plastein level in enzymic degradation, they 

 are of uniform constitution. Lavroff (242, 243) certainly obtained the 

 precipitation as other authors have done, and he called the substance 

 shortly "coagulose". He found that it could be produced from diges- 

 tive products from which the hexone bases had been removed, and that 

 the product which was formed, contained no such bases. It was also 

 formed from material in which these bases were present, and in this 

 case the coagulose contained them. He was not therefore inclined to 

 regard them as specific substances. In a later paper (244) he demon- 

 strated that, by the peptic digestion of caseinogen, two series of 

 "coagulose" substances were formed, one conforming to a proteose 

 type, the other to a polypeptide type. 



Sacharoff (345) held, that this plastein formation was not synthetic 

 in origin at all, that it was only an intermediate substance in the pro- 

 cess of digestion, precipitation taking place simply because the physical 

 conditions for solution were not suitable. Bayer (56) also stated that, 

 in his opinion, the substance formed was no true synthetic product, 

 and thought that its protein-like character was probably due to im- 

 purities. He believed that it was a member of the so-called peptoid 

 group of Zunz, and that it was a body therefore of comparatively 

 simple constitution. Herzog (191) and Volhard (412) maintained 

 that this plastein formation was not the result of the action of rennin 

 at all, but might be regarded as another example of the reversibility 

 of reaction of proteolytic ferments (Herzog) or of pepsin (Volhard). 



The question as to (i) whether this substance is a new synthetic 

 product differing from the protein from which the proteoses are derived, 

 or (2) whether it is merely a resynthesis of the original protein from 

 which the proteoses are obtained, or (3) whether it is no synthetic 

 product at all but merely a substance a digestion product on the 

 road to complete solution is not definitely settled. The work, how- 



