PRESIDENTIAL ADDRESS. 451 



specific type of activity ; the organism, whatever its nature may be, which 

 causes measles cannot give rise to small-pox, nor vice versa, but each breeds 

 as true to type as do lions and leopards. 



The essential and distinctive characteristic of a living body of any kind 

 whatsoever is that it exhibits while it lives permanence and continuity of 

 individuality or personality, as manifested in specific behaviour, combined with 

 incessant change and lability of substance ; and further, that in reproducing 

 its kind, it transmits its specific characteristics, with, however, that tendency 

 to variability which permits of progressive adaptation and gradual evolutionary 

 change. It is the distinctively vital property of specific individuality combined 

 with ' stuff-change ' (if I may be allowed to paraphrase a Teutonic idiom) 

 which marks the dividing line between Biochemistry and Biology. The former 

 science deals with substances which can be separated from living bodies, and 

 for the chemist specific properties are associated with fixity of substance'; but 

 the material with which the biologist is occupied consists of innumerable living 

 unit-individuals exhibiting specific characteristics without fixity of substance. 

 There is no reason to suppose that the properties of a given chemical substance 

 vary in the slightest degree in space or time; but variability and adaptability 

 are characteristic features of all living beings. The biochemist renders inesti- 

 mable services in elucidating the physico-chemical mechanisms of living 

 organisms; but the problem of individuality and specific behaviour, as mani- 

 fested by living things, is beyond the scope of his science, at least at present. 

 Such problems are essentially of distinctively vital nature and their treatment 

 cannot be brought satisfactorily into relation at the present time with the 

 physico-chemical interactions of the substances composing the living body. 

 It niay be that this is but a temporary limitation of human knowledge pre- 

 vailing in a certain historical epoch, and that in the future the chemist will 

 be able to correlate the individuality of living beings with their chemico- 

 physical properties, and so explain to us how living beings first came into 

 existence; how, that is to say, a combination of chemical substances, each 

 owing its characteristic properties to a definite molecular composition, can 

 produce a living individual in which specific peculiarities are associated with 

 matter in a state of flux. But it is altogether outside the scope and aim of 

 this address to discuss whether the boundary between biochemistry and biology 

 can be bridged over, and if so, in what way. I merely wish 'to emphasise 

 strongly that if a biologist wishes to deal with a purely biological problem, 

 such as evolution or heredity, for example, in a concrete and obiective manner! 

 he must do so in terms of living specific individual units. It is "for that reason 

 thati shall apeak, not of the chromatin-substance but of chromatinic elements, 

 particles or units, and I hope that I shall make clear the importance of this 

 distinction. 



To return now to our chromatin ; I regard the chromatinic elements as beino- 

 those constituents which are of primary importance in the life and evolution 

 of living organisms mainly for the following reasons : the experimental evi- 

 dence of the preponderating physiological role played by the nucleus in the 

 life of the cell; the extraordinary individualisation of the chromatin-particles 

 seen, universally in living organisms, and manifested to a degree which raises 

 the chromatinic units to the rank of living individuals exhibiting specific 

 behaviour, rather than that of mere substances responsible for certain chemico- 

 physical reactions in the life of the organism ; and last, but by no means least, 

 the permanence and, if I may use the term, the immortality of the chromatinic 

 particles in the life-cycle of organisms generally. I will "now deal with these 

 points in order; my arguments relate, in the first instance, to those organisms 

 in which the presence of true cell-nuclei renders the identification of the 

 chromatin-elements certain, as pointed out above, but if the arguments are 

 valid in such cases they are almost certainly applicable also to those simpler 

 types of organisms in which the identification of chromatin rests on a less 

 secure foundation. 



The results obtained by physiological experiments with regard to the 

 functions of the nuclear and cytoplasmic constituents of the cell are now 

 well known and are cited in all the text-books. It is not necessary, therefore 

 that 1 should discuss them in detail. I content mvself with quoti'nrr a compe- 

 tent and impartial summary of the results obtained": 



G 2 



