492 SESSION V. DISCUSSION 



in showing, the propagation of the excitation along the nerve fibre corresponds to a wave 

 of structural processes, altering the mechanical and optical properties of the nerve fibre, 

 and is accompanied by a thickening of the nerve by about a twenty-thousandth of its 

 diameter. This minute thickening is propagated at the same rate as that of the wave of 

 excitation during summation, each individual excitation impulse may even be demon- 

 strated by means of the interference microscope. Any objects, no matter how simple, if 

 they are observed with sufficient care, show structural reorganization, sometimes fast, 

 sometimes slower, associated with changes in chemical mechanism. In speaking of the 

 origin of self-maintaining chemical processes in biopoesis and the structures corresponding 

 with them, one must, at some quite early stage in the development of proto-organisms, 

 also take account of structural motility, not only as forming the basis for the growth and 

 development of the organisms, but also as forming that of their functional adaptation to 

 rapid changes in the external environment. 



One must ask what part is played by this apparently more or less universal property of 

 the motility of living structures. I should like, here, to make an analogy, while fully 

 recognizing the danger of such a formulation of the question. Contemporary technology 

 has led to an extensive working out of the theory of automatically self-regulating systems 

 which build up complicated aggregates, making use, at each particular moment, of the 

 most favourable available conditions, and changing themselves with changing circum- 

 stances. Regulation of this sort is fundamental to the so-called 'feed-back' principle, i.e. 

 forward and backward interactions within a functioning system. Is there no interde- 

 pendence between structures and the metabolic functions which they subserve, and, 

 conversely, no dependence of metabolic processes on the structural organization of the 

 living thing ? Is there nothing similar to such a feed-back which gives rise to the remark- 

 able regulating mechanism which is characteristic of living things ? 



S. W. Fox (U.S.A.): 



Comment i. — It is of interest to compare some of the knowledge in the field of proteo- 

 lytic enzymes with the proposal of Dr Straub. It is unnecessary to mention the work of 

 Northrop and co-workers. Desnuelle and others have recently shown that chymotrypsin 

 and trypsin, usually thought of as being specifically different, each have N-isoleucylvalyl 

 dipeptides in the structure. This seems to be quite consistent with Dr Straub's proposal. 

 It should be added that in the U.S.A. Michael Laskowski, Jr, has found a small amount 

 of chymotryptic activity in trjrpsin which he claims cannot be explained by contamination 

 of trypsin by chymotrypsin. 



Comment 2. — I believe that many of us have been overwhelmed for many years by the 

 potentialities of protein isomerism. As we have learned to assess the actual diversity of 

 protein molecules (see S. W. Fox, Amer. Scient., 44,347, 1956) we find a highly limited 

 diversity of protein molecules, analogously to Dr Bernal's description of physical 

 structures. 



This situation, to put it necessarily in qualitative form, poses the problem of how to 

 explain the great diversity of organisms on a foundation of relatively narrow diversity of 

 macromolccular types. 



I believe the answer is to be found in the interactions of protein molecules, of which 

 Dr Dcborin spoke. Interactions of a limited variety of protein molecules among them- 

 selves, or with a probably even more limited variety of nucleic acid molecules, could 

 provide an exponentially very much greater number of phenotypes. 



F. SoKOL (Czechoslovakia): 



The Formation of Bonds between Proteins and Nucleic Acids 



In connection with Prof. Deborin's paper and Prof. Tongur's contribution to the 

 discussion I should hke to make the following comment. It seems to me that, in artificial 



