Inheritance Materials of Germ-Cells 71 



a latent state, of tlie progenitors of the developing in- 

 dividual. 



Investigation of the first of these j)roblems is to a large 

 extent a matter of observation, as we have seen in the pre- 

 ceding pages. The sub-science of histogenesis consists 

 largely in tracing out the processes by which completed 

 tissues arise by the transformation of less differentiated or 

 undifferentiated cells. And when such newly arisen tissues 

 and structures are proved to be hereditary by such evi- 

 dence as we have called attention to, then the study of 

 histogenesis comes to be so far a study of hereditary sub- 

 stance. 



When, however, we turn to the other problem, that of 

 how hereditary substance comes to be such, we are in a 

 different, a much more difficult case, for so far science has 

 succeeded in getting almost no obsei'vational hold upon it; 

 and despite the vast discussion it has received the darkness 

 that envelops it is hardly an iota less black than it was the 

 day of its original formulation. But stygian as the darkness 

 is, here, especially as to details, we yet are able to see, 

 probably, the quarter from which light will come if ever it 

 does come. That quarter is the physical-chemistry con- 

 ception of the organism as a system of phases the whole of 

 which, as a species entity, is essential to its equilibrated 

 activities. This nature of the organism, together with some- 

 thing akin to its internal secretory and enzymic productiv- 

 ity, enables it, we may conjecture, by some means now 

 wholly unknown, to reflect its totality of transferable at- 

 tributes upon the germinal cells and to transform thrni into a 

 latent state. Ungrudging acknowledgment of the complete- 

 ness of our ignorance of how any part of a cell or any other 

 portion of an organism becomes endowed witli the capacity to 

 develop or causally to affect the development of an organism 

 similar to that from which it came, should he an important 

 item in the preparation to accept any and all indubitable 



