86 PROBLEMS OF GENETICS 



even of the haziest sort as to the nature of living organisms, or 

 of the proximate causes which determine their forms, still less 

 can we attempt any answer to those remoter questions of origin 

 and destiny which form the subject of the philosopher's con- 

 templation. It is in no spirit of dogmatism that I have ventured 

 to indicate the direction in which I look for a solution, though 

 I have none to offer. It may well be that before any solution 

 is attained, our knowledge of the nature of unorganised matter 

 must first be increased. For a long time yet we may have to 

 halt, but we none the less do well to prepare ourselves to utilise 

 any means of advance that may be offered, by carefully recon- 

 noitering the ground we have to traverse. The real difficulty 

 which blocks our progress is ignorance of the nature of division, 

 or to use the more general term, of repetition. 



Let us turn to the more familiar problem of the causes of 

 variation. Now since variation consists as much in meristic 

 change as in alteration in substance or material, there is one 

 great range of problems of causation from which we are as yet 

 entirely cut off. We know nothing of the causation of division, 

 and we have scarcely an observation, experiment or surmise 

 touching the causes by which the meristic processes may be 

 altered. 



Of the way in which variations in the substantive composition 

 of organisms are caused we have almost as little real evidence, 

 but we are beginning to know in what such variations must con- 

 sist. These changes must occur either by the addition or loss 

 of factors. 



We must not lose sight of the fact that though the factors 

 operate by the production of enzymes, of bodies on which these 

 enzymes can act, and of intermediary substances necessary to 

 complete the enzyme-action, yet these bodies themselves can 

 scarcely be themselves genetic factors, but consequences of their 

 existence. What then are the factors themselves? Whence do 

 they come? How do they become integral parts of the organism? 

 Whence, for example, came the power which is present in a White 

 Leghorn of destroying probably reducing the pigment in its 

 feathers? That power is now a definite possession of the breed, 



