96 ADAPTATION AND DISEASE 



their growth would show a greater affinity for the radicles whose 

 constitution lead to the appearance of recessive qualities. 



The existence of determinants as entities, as I have demon- 

 strated, cannot on physical grounds be accepted, and if in their 

 place we accept differences in the constitution or arrangement 

 of individual radicles composing essential portions of the com- 

 bined and complex molecules of living matter, it is still possible 

 to interpret the facts of Mendelism and indeed interpret not a 

 few phenomena which by the hypothesis of determinants cannot 

 be explained. 1 



Summary 



However, I realize that here I advance into regions outside 

 the boundaries of current medical thought. To sum up, it may 

 be said that, according to this hypothesis, each species must be 

 regarded as having for its essential living matter a distinct 

 organic compound, a compound as distinct as any inorganic salt, 

 but differing from that simpler inorganic salt in that, whereas 

 the central ring or chain is of relatively fixed constitution, the 

 radicles composing that ring or chain are capable of attracting 

 and then of reproducing a series of side-chains which may vary, 

 so that within the species there may be various strains, just as 

 we may speak of various strains of crystalline haemoglobin being 

 obtained from different samples of human blood. 



Let me freely admit that the diagrams here afforded are 

 very crude. With the necessarily condensed presentation of 

 my subject they have seemed to me essential. To those un- 

 familiar with the advanced organic chemistry of to-day, to have 

 attempted illustrations of the successive stages of my argument 

 by elaborate graphic chemical formulae would have been worse 

 than useless. I shall be satisfied if I have rendered it clear that 

 it is possible to replace an impossible hypothesis based upon sup- 

 posititious independent and transposable determinants by one 

 based upon what we know of the composition and physical 



1 Of set purpose, as being outside the scope of my earlier work and of medical 

 research, I did not in the course of these lectures refer to the newer studies of 

 the last few years upon differentiation of the individual chromosomes. Such 

 differentiation with localization of groups of unit characters in particular 

 chromosomes is, I would point out, distinct from Weismann's determinants. 

 I hope to take up this matter later. 



