260 CONCLUSION [CH. 



success is only achieved, and a great human advance made, 

 when they meet and discover that their work has all along 

 been one. And when cytology becomes experimental, it 

 will come into contact immediately, not only with other 

 branches of Biology, but with the still more general facts 

 and laws of Chemistry and Physics. Cytology touches at 

 every point the fundamental problems of the chemical and 

 physical basis of life, and whether the mechanistic or the 

 vitalistic theory be the true one, it is equally important to 

 discover the chemical and physical relations of living matter. 

 Whether the living differs from the inorganic only in its 

 greater complexity, or whether life is something unique 

 and inexplicable in terms of matter and energy, it remains 

 true that living things are composed of matter and obey 

 the laws of energy, and in every branch of cytology the 

 student is brought up against these laws for an explanation 

 of the phenomena he observes. A conspicuous example of 

 this is given by the various hypotheses of cell and nuclear 

 division ; osmosis, surface-tension, electricity, and a hypothe- 

 tical form of energy named provisionally " mitokinetism " 

 have all been invoked to account for the facts, and only a 

 fuller knowledge of the action of physico-chemical forces in 

 living matter can provide the answer to the riddle. Again, 

 in the phenomena of fertilisation and parthenogenesis, some 

 observers explain the facts in terms of chemistry, supposing 

 that the spermatozoon or the parthenogenetic agent intro- 

 duces substances into the egg, while others point to a 

 physical explanation, and ascribe the changes to an altera- 

 tion of the electrical conductivity of the egg-surface. Even 

 in the most elementary practice of cytology, in the fixation 

 of cells for microscopic examination, it is only by some 

 knowledge of the physics and chemistry of colloids that we 

 can decide with confidence whether we are observing natural 



