28o LIFE AND DEATH. 



and besides, with very few exceptions — those of 

 cadmium, mercury, and the gases of the argon series 

 — the atoms of simple bodies cannot exist in a free 

 state. 



Thus, as in the vital struggle, the ambient medium 

 by means of alimentation furnishes to the living being, 

 whether whole or fragmentary, the materials of its 

 organization and the energies which it brings into play. 

 It also furnishes to brute bodies their materials and 

 their energies. 



It is also said that the ambient medium furnishes 

 to the living being a third class of things, the 

 stinmli o{ lis activities — i.e., its "provocation to action." 

 The protozoon finds in the aquatic environment 

 which is its habitat the stimuli which provoke it to 

 move and to absorb its food. The cells of the 

 metazoon encounter in the same way in the lymph, 

 the blood, and the interstitial liquids which bathe 

 them, the shock, the stimulus which brings their 

 energies into play. They do not derive from them- 

 selves, by a mysterious spontaneity without parallel 

 in the rest of nature, the capricious principle which 

 sets them in motion. 



Vital spontaneity, so readily accepted by persons 

 ignorant of biology, is disproved by the whole history 

 of the science. Every vital manifestation is a response 

 to a stimulus, a provoked phenomenon. It is un- 

 necessary to say this is also the case with brute 

 bodies, since that is precisely the foundation of the 

 great principle of the inertia of matter. It is plain 

 that it is also as applicable to living as to inanimate 

 matter. 



