Understanding of the Nature of Life BK 
such an understanding must be reduced to comparing 
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 
would 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 af rebuilding 
the partially decomposed protoplasmic substance. And 
to this alteration of different affinities, the opposite proto- 
