Understanding of the Nature of Life 335 



such an understanding must be reduced to comparing 1 

 vital phenomena with some physico-chemical model al- 

 ready known, suitably modified by the particular special 

 conditions imposed upon it so that just these special con- 

 ditions shall determine the differences which exist be- 

 tween this vital phenomenon and the phenomenon of the 

 inorganic world most closely related to it. If this be 

 so, it is then the duty of science emphatically to reject 

 such a denial of scientific thought as the renunciation 

 of the quest of this understanding would constitute. 

 Whether one clearly recognizes it or not, it is just this 

 search for the nature of the vital principle which properly 

 constitutes the principal object and the final goal of all 

 biologic study in general. 



Others again are not willing to accord to life even 

 the slightest property which should not be simply physico- 

 chemical in nature. Among all these it is enough to 

 cite the example of Verworn who not only relegates 

 assimilation to the category of purely chemical phe- 

 nomena, by means of his "Biogen" hypothesis, but who 

 \vould explain protoplasmic currents, the protusion of 

 pseudopodia, the movements of cilia, and in general all 

 movements of living beings by a double and alternative 

 chemotropism of protoplasmic substance rather than by 

 currents of nervous energy. Protoplasmic substance, in 

 fact, according as it remains unstimulated or is stimu- 

 lated, that is, partially decomposed by the stimulus which 

 would agitate it mechanically, would possess a chemical 

 affinity for the oxygen of the environment or for the 

 substances produced by the nucleus capable of rebuilding 

 the partially decomposed protoplasmic substance. And 

 to this alteration of different affinities, the opposite proto- 



