172 SECTIONAL ADDRESSES. 



attributes of life is that it is a dynamic condition, it does become possible 

 to form a conception of protein synthesis in relation to that fact. The 

 experiments of Willstatter and others have shown that to some extent the 

 specificity of enzymes is accounted for by the ' carrier ' with which they 

 are associated. It is not inconceivable that a catalyst capable of bringing 

 about the union of amino-acids in the living cell and ultimately fashioning 

 its protoplasm may be attached to or associated with a ' carrier ' which, 

 instead of having a fixed configuration, as with the enzymes that we can 

 extract from the dead cell, has one which is continually varying, this 

 dynamic state being characteristic of the living material of the cell. 



If, further, we could assume that the variations in the configuration of 

 the carrier were cyclic, always going through a definite series of phases, 

 it might be possible to account for the fact that at any particular phase 

 of the cycle the configuration would be such as to favour the synthetic 

 union of one particular amino-acid rather than any other because of its 

 spatial arrangement. The assumption of cyclic changes in simple or 

 complex living organisms is not new in Physiology, and it is not unlikely 

 that they occur in parts even of the cell itself. The phenomena of mitosis 

 are a somewhat gross illustration of such cyclic events. 



It is perhaps difficult to justify speculations of this kind, but it appears 

 to me that it is at least useful as an intellectual exercise to try and arrive 

 at some conception, founded on what little experimental evidence we at 

 present possess, of a possible mechanism which would account for the 

 reproduction time after time of the intricate pattern of the protein of a 

 particular type of cell. 



Whatever be the mechanism of protein synthesis there is another fact 

 concerning it which is of interest, and that is that the cell to maintain itself 

 must apparently contain a certain concentration of amino-acids. If these 

 are not supplied in the animal's food then the animal supplies them by 

 maintaining its more important tissues at the expense of others. This 

 would suggest that the conditions for nitrogeneous equilibrium which we 

 find in the whole animal have their replica in each cell, but the concentra- 

 tion of amino-acids required to maintain the equilibrium is not the same 

 for all. Hence an amino-acid deficiency such as occurs in protein starva- 

 tion leads to autolysis of some tissues before others. The equilibrium 

 conditions appear to be set at difierent levels. The fact that certain 

 amino-acids are more necessary than others in providing for this balance 

 may be partly due to their special importance in the protoplasm of those 

 cells which are the first to break down when protein food is withdrawn or 

 an inadequate protein is fed. 



The possibility that protein synthesis is associated with some part of 

 the cell which is undergoing cyclic changes, and is thus alive, raises the 

 interesting question of the site of this and possibly other syntheses, such 

 as those of fat and glycogen. Are all parts of the cell, that is to say, both 

 nucleus and protoplasm, to be regarded as alive in the sense I have 

 indicated, and therefore to be considered as regions in which syntheses 

 depending on life can be brought about ? 



It is necessary not to confuse the terms irritability and life. It is true 

 that what we term irritability is usually taken to imply that the tissue 

 which shows it is living, but taking the nerve fibre as an example, it would 



