PRESIDENTIAL ADDKESS. 525 



In cases of greater complexity, where no doubt in course of time the same 

 method of indirect attack will be adopted, in preparation for this event, the 

 necessities of the moment largely confine our attention to a discovery of the 

 various parts present in these mechanisms. In fact, the first requirement is a 

 knowledge of the micro-chemistry of these more complex structures, that is to 

 say, a precise knowledge of the chemical materials distributed in minute spaces 

 of microscopical dimensions. It is well known that my predecessor in this 

 honourable post, Professor Macallum, of Toronto, has contributed largely to our 

 knowledge of these matters, and that he further assisted us to a right conception 

 of the forces in action between these minute masses of material by his excellent 

 Presidential Address to this Section. 



Thinking of the body as no more than a collection of chemical reactions, this 

 elaborate separation of parts in a multiplicity of extremely small spaces protects 

 the individuality of a certain large number of reactions, whilst at the same 

 time securing a rich maintenance of contact with supplies of raw material and 

 a ready means for separating the end-products of reactions from the materials 

 in reaction at each point. Every nucleus, surrounded by its constellation of 

 secondary chemical reactions, is thus given certain limits of size, surface, terri- 

 tory, and environment. These are physical necessities of arrangement possible 

 within the conditions of solution met with in the body, and no doubt largely 

 due to physical states developed by each reaction — that is to say, that the 

 products of each reaction exert a physical influence and produce characteristic 

 physical arrangements. It is not without interest, to realise that cell-growth, 

 and the increase in nuclear surface with which it is attended in cell-division, 

 is apparently initiated at every centre by what is doubtless a physical process, 

 and what, as Loeb has shown us, may be accelerated by definite physical 

 change. Such effects of growth are best studied in those early days of enormous 

 expansion when the ovum increases to one thousand million times its original 

 weight, and it is at this time that these separative physical consequences of 

 chemical reactions are most apparent. 



During this primary expansion not only have the reactions of nuclear matter 

 been extended to occupy some hundred million times more mass, but it is also 

 true that they have been modified in a very large number of ways, and doubtless 

 this as the consequence of special conditions, extrinsic conditions, existing at 

 the time of formation of each separate part. These modifications are largely 

 shown by differences in appearance and structure, and are each attended by some 

 difference in the function of typical groups of cells. A singular persistence 

 in the similarity of structure and function exhibited by successive generations 

 of similarly placed cells is no doubt sometimes due to the maintenance of 

 those special extrinsic conditions which occasioned their initial modification. In 

 these cases reversion to an original type may occur on immersion in formerly 

 pre-existent conditions, and indeed a whole series of different structures make 

 their appearance as the conditions are further variously modified, as is sometimes 

 seen in the regeneration of parts. 



There is, however, seen in some cases a greater degree of persistence, studied 

 for example in malignant growths, which is largely retained even when the ex- 

 trinsic conditions are greatly modified; and in such cases there has doubtless 

 occurred some elimination and refinement — that is to say, rather an abstraction 

 than an addition of character — as the consequence of the initial modification. 



In certain places in the adult, physical conditions due to the modification and 

 acceleration of chemical reactions are still frequently provocative of nuclear 

 growth and subdivision : thus in the tonsils, follicles, patches, and lymphatic 

 structures generally that are embedded in the surface of the alimentary canal. 

 These structures, characterised by their great wealth of nuclear material, experi- 

 ence great nuclear change, to which they are largely stimulated by chemical 

 substances derived from foreign organisms. Specifically affected by each chemi- 

 cal substance, they are probably the site of manufacture of specific neutralising 

 substances that are driven from these sites of activity into the portal system 

 almost as soon as the substances exciting their appearance are driven in from 

 the absorbent surface of the alimentary canal. 



In other places in the adult, however, such conditions never recur after a 

 certain date in development. In these places the nuclear material has been 

 so refined as to be irresponsive to conditions that accelerate and modify the 



