Law of Proenvironment 233 



ory, of instinct so-called, of intelligence, and of reason, all 

 of which are e\ddently associated with and center round nerve- 

 cells. 



The question therefore at once presents itself: Wherein 

 does such a nerve-cell differ from other nucleated body cells, 

 all of which we would class as bio-cognitic? In any attempted 

 explanation graded stages of developmental or evolutionary 

 complexity should probably be traceable, that lead insensibly 

 upward to the most complex nervous or mental acts. At the 

 foundation of all such action we would propose a principle 

 that might be expressed as '*the recurrent periodicity of def- 

 inite organic molecular vibrations." The beginnings of such 

 seem to be traceable in some phenomena of plant life, and are 

 wholly and invariably originated by changes in environal 

 stimuli. Thus the experiments of Darwin, Pfeffer, and Ulrich 

 demonstrate that in plants which show nyctitropic move- 

 ments, if the plants be kept beyond the normal period in dark- 

 ness, rhythmic change occurs about the time when the normal 

 lumic stimulus that is now lacking should have acted. So 

 plants kept continuously for two to four days in the dark 

 will "wake up" about the normal period when light should 

 have reached them. But, if the periodic waves or rhythms 

 of alternate light and darkness be upset, after six to eight 

 days the plants become unhealthy and decay. 



Again the annual or even more frequent seasonal formation 

 of reproductive cells appears often to proceed with rhythmic 

 regularity, even though some of the primary exciting stimuli 

 are absent. In other words there is registered in the living 

 cells such a rhythmic time relation that, in absence of some of 

 the factors that constitute the complete stimulus, response 

 action may be shown. Even in the simpler metazoan animals 

 the rhythmic recurrence of hunger and of satisfied states, of 

 active and of passive existence, of accumulation of waste 

 material and of expulsion of it, of mating and of alternating 

 isolated life, as well as otlier phenomena that %\dll occur to 

 all, including the "habits" — so-called — in higher animals, are 

 similar exhibitions of rhythmic stimulation. 



8* 



