I.— PHYSIOLOGY. 171 



Taylor's production of a protamine by a glycerol extract of clam liver from 

 the products of its complete hydrolysis. 



But, so far as I am aware, this is an isolated observation which has 

 not been extended or repeated with other protamines. The other is the 

 preparation of so-called plasteins from the products of the partial hydro- 

 lysis of certain proteins by pepsin. A comprehensive review of the subject 

 of plastein formation by Wasteneys and Borsook, who have themselves made 

 notable contributions to this problem, has led them to the belief that in 

 this phenomenon we have a true resynthesis of protein from some of the 

 more complex of its hydrolytic products. Apparently only certain of 

 these yield plastein on treatment in highly concentrated solution with 

 pepsin under appropriate conditions, and the distinctive feature in them 

 which makes plastein formation possible has not yet been discovered. It 

 seems probable that it is both a property of certain proteoses and of pepsin 

 that enables the synthesis to occur, and some evidence for this view is 

 provided by the observation of Wasteneys and Borsook that the formation 

 of bodies similar to plastein is brought about when benzene and some other 

 substances are emulsified in a peptic digest of egg albumen. The plasteins 

 obtained in this way have different physical properties from those obtained 

 by the action of pepsin on similar digests. Wasteneys and Borsook suggest 

 that this may incficate how differences in composition of the proteins 

 synthesised by the organism are produced, certain proteose substrates 

 being specifically adsorbed on particular surfaces in the cell and then 

 undergoing reaction to form the synthetic product. Even if this be 

 accepted as a possible explanation it still leaves many questions regarding 

 protein synthesis unanswered, and not the least difficult of these is the 

 problem of how the separate amino-acids are brought together to form the 

 specific proteose substrates which one must postulate as combining — and 

 in a definite order — to produce the particular protein which is characteristic 

 of the cell which synthesises it. One of the great difficulties in accounting 

 for the synthesis of protein by a reversal of enzyme action is that this 

 synthesis only takes jslace, so far as we can observe, in a cell which is living. 



The process by which the substance of the cell is increased, the building 

 up of protoplasm, is one which must be closely allied to protein synthesis, 

 since the material we call protoplasm is constituted for the greater part of 

 amino-acids, united, so far as can be ascertained, by the same sort of 

 linkage that we find in proteins. The protoplasm of the dead cell responds 

 to all the tests by which we identify protein, it is subject to the action of 

 hydrolytic agents in the same way and yields identical products when 

 hydrolysed. 



Ought we not therefore to look for some of the mechanisms of protein 

 synthesis in the processes which operate M^hen the living cell grows, and 

 can we by any stretch of imagination account for this by a reversal of the 

 action of one or more hydrolytic enzymes ? 



It appears inconceivably difl&cult to do so. The extreme specificity 

 of the reaction which necessitates that at a given phase of the synthesis 

 one particular amino-acid and that one alone can be added as the next 

 link in the molecule, requires such a multiplicity of enz^nnes and such a 

 remarkable degree of control of their action as to be almost outside the 

 range of probability. When we remember, however, that one of the prime 



