174 SECTIONAL ADDRESSES. 



synthesis of proteins whicli are not labile like the protoplasna of, say, the 

 muscle or nerve cell. Their formation, however, may be due to the opera- 

 tion of the same general process. They are certainly non-irritable and 

 non-living. It is difficult to imagine that while in the cell they possess the 

 power of reproduction but lose it once they have been cast out. 



If we accept the possibility that the nucleus of the cell may be the 

 site of protein synthesis it is legitimate to consider whether the substances 

 which appear in the protoplasm as discrete particles or masses such as 

 glycogen or fat are produced in the nucleus or only in the protoplasm. 

 We have no evidence as to this. The fact that they first appear as visible 

 objects in the protoplasm is not evidence that they were produced there, 

 and it has already been pointed out that their synthesis is apparently only 

 possible in cells which are alive. They may be synthesised in the nucleus 

 and stored in the protoplasm. Their disappearance from time to time 

 may be conditioned by the liberation of enzymes from the nucleus to 

 hydrolyse them. Such a view would do away with some of the difficulties 

 which we experience in attempting to explain why substrates may be 

 present in cells which, judged by their behaviour after death, appear to 

 contain enzymes that hydrolyse them. The protoplasm, instead of pro- 

 ducing such reserve materials, may serve as a convenient storehouse for 

 them until the appropriate stimulus for their breakdown arrives. 



One property of proteins, which may account in a general way for 

 the presence of protein-like structure in protoplasm, is their buffering 

 power. The nucleus is probably the most labile part of the cell. The 

 chemical reactions proceeding in it may demand an euArironment that has 

 to be finely controlled as regards changes in reaction or the concentration 

 of certain ions. The protoplasm may thus serve as a protective layer 

 between the nucleus and the external world, guarding it from changes 

 which would otherwise terminate its existence. The known properties of 

 the proteins, both chemical and physical, may be useful to this end, to 

 which they are almost ideally suited. 



Even if we can accept as possible the unorthodox view that the nucleus 

 is the only living part of the cell, and is therefore the only part that can 

 bring about syntheses which depend upon life, it does not solve our diffi- 

 culties in explaining how they are achieved. It merely narrows down the 

 possible sites in the cell in which they occur. The nucleus itself is a 

 complex structure, and we have as yet few experimental methods for 

 elucidating it. Most biologists would, I think, agree that the cell has 

 arisen by a process of evolution from something simpler and eventually 

 from non-living materials. It cannot have come as a ' bolt from the 

 blue.' If we regard the nucleus as the only living part of the cell, then we 

 may justly regard the protoplasm as something that has been acquired 

 or developed in the process of evolution and is now necessary to its exis- 

 tence. We do not know definitely, however, of nuclear material which is 

 living and devoid of its protoplasmic envelope unless such an arrangement 

 is present in the bacteria. But the investigation of filterable viruses has 

 given an indication • that material possessing the prime attribute of life, 

 namely, the power of reproducing itself, exists, possibly in simpler forms 

 than we find in the smallest visible organisms. 



If we agree that the cell has evolved from something simpler, then we 



