CONCLUSION 283 



We know, for example, that certain cells of the reproduc- 

 tive glands^ have a profound and commanding influence on 

 all the body cells, including even the brain-cell centres of 

 thought and intelligence — all this is, in a sense, an outflowing 

 from the heredity-germ region, a centrifugal interaction. Is 

 there any reversal of this process, any inflowing or centripetal in- 

 teraction whereby chemical messengers from any part of the 

 body specifically affect the heredity-germ, and thus the new or- 

 ganism to which it will give rise? This is one of the first 

 things to be ascertained by future experiment. 



Being still at the very beginning of the problem of the 

 causes of germ evolution — a problem which has aroused curi- 

 osity and baffled inquiry throughout the ages — it were idle to 

 entertain or present any settled conviction in regard to it, 

 yet we cannot avoid expressing as our present opinion that 

 these causes are internal-external rather than purely internal — 

 in other words, that some kind of relation exists between the 

 actions, reactions, and interactions of the germ, of the organ- 

 ism, and of the environment. Moreover, this opinion is prob- 

 ably capable of experimental proof or disproof. 



We may well conclude with the dictum of Francis Bacon,^ 

 one of the first natural philosophers to counsel experiment, 

 who in his Novum Organum (1620) shows that living objects 

 are well adapted to experimental work, and points out that it 

 is possible for man to produce variations experimentally: 



'' They [i. e., the deviations or mutations of Na- 

 ture] difer again from singular instances, by being 

 much more apt for practice and the operative branch. 

 For it would be very difficult to generate new species, 

 but less so to vary known species, and thus produce 



' Goodale, H. D., 1916; Lillie, Frank R., 191 7. 

 ^ Bacon, Francis, 1620, book II, sec. 29, p. 180. 



