424 EDMUND B. WILSON 



cular side-chains or molecular 'Bausteine,' so the addition, subtraction 

 or substitution of particular 'determiners' or 'factors' in the zygote 

 calls forth specific responses that lead to the production of corresponding 

 characters. The reasoning that applies to the first of these cases seems 

 equally applicable to the second. No one, I suppose, would hold in the 

 first case that the particular molecular groups or ' Bausteine' concerned 

 in the change are 'bearers of (i.e., are alone responsible for) the result- 

 ing new qualities. The qualities of any protein, as Kossel has recently 

 urged, belong to the molecule as a whole, and are not to be regarded as 

 the sum of the qualities of its constituent 'Bausteine.' Why should we 

 regard in a different light the 'determiners' (chemical substances?) 

 concerned in the second case? They are, clearly, not to be regarded as 

 'bearers' or 'physical bases' of the characters which depend upon their 

 presence or absence. They are, I repeat, only differential factors of 

 ontogenetic reactions that belong to the germ considered as a whole or 

 unit-system" (Wilson, '12). 



Kossel ('12) makes the pregnant remark that every peculiarity of 

 the species and every occurrence affecting the individual may be 

 indicated by special combinations of protein 'Bausteine.' The 

 facts lead us to seek for such compounds (substances) in the chro- 

 matin or the chromosomes. It can hardly be said that even a 

 beginning has been made-in the chemical investigation of the dis- 

 tribution of the chromatin-substances within the nucleus. Cyto- 

 logically, however, a long series of the most significant facts have 

 been made known in respect to their groupings and modes of dis- 

 tribution. Evidence steadily accumulates that these processes 

 are perfectly ordered; and the fact is now more than ever evident 

 that they run parallel to the factors of determination and heredity. 

 There has been a disposition on the part of certain writers of 

 late to minimize the definite order of the morphological trans- 

 formations of the nucleus (cf . Fick, '07, Delia Valle, '09) ; and 

 these authors, among others, have undoubtedly helped to create 

 an impression that these phenomena, particularly as regards the 

 chromosomes, are too vague and fluctuating to afford trustworthy 

 results on the side of cytological research. I believe this to be a 

 backward step, though I am very ready to admit the service to 

 accuracy of observation that may be rendered by so critical and 

 sceptical a spirit. Plastic, and in some respects variable like 

 other biological phenomena, these processes undoubtedly are; but 

 the more one studies them in detail the stronger grows the con- 



