THE BEGINNINGS OF LIFE. 371 



utterly impossible that the matter which undergoes such 

 changes should continue to exist under the form of an 

 Alga. But, although changes of this kind have been set 

 up although altered modes of molecular activity have 

 been induced in response to new external pulses or move- 

 ments surely there is no reason for supposing that the 

 matter of which such an organism is composed must 

 necessarily c die/ simply because it can no longer exist 

 under its old form. 



As we have already endeavoured to show \ the death 

 of an animal, from a physical point of view, merely 

 means the cessation of those particular actions and re- 

 actions which were accustomed to go on in its body, 

 and which are essential to its existence as such an 

 organism. Its organic structure had been produced 

 under their influence, and its form could not be main- 

 tained without their continuance. Its several tissues 

 had been built up, and were what they were, solely 

 on account of their relations to one another and of 

 the mutual performance of certain functions more or 

 less necessary for the well-being of the organism as 

 a whole. Let the throbbings of the heart cease for 

 a while, and the highly-organized vertebrate animal 

 dies. Pabulum is no longer supplied to its elementary 

 parts, and, as minute by minute passes by, changes 

 take place in its most sensitive tissues, which render 

 a renewal of the life-giving conditions more and more 

 difficult. At last it becomes impossible again to set 



1 See vol. i. pp. 108-112. 

 B b 2 



