THE BEGINNINGS OF LIFE. 183 



This division may remind the reader of our classifi- 

 cation of fermentative processes ^. The analogy existing 

 between them is very close, so close, indeed, that we 

 should have been quite entitled to have set down a 

 third class of processes under the name of Analytico- 

 Synthetic Heterogenesis. We wish, however, to sim- 

 plify our statements as much as possible, so that for the 

 present we make no further comments on this latter 

 possible division of the subject. The analogy which 

 exists between Synthetic Fermentation and Synthetic 

 Heterogenesis will be much more fully understood after 

 the perusal of the next chapter ; meanwhile it may be 

 useful for us to make a few remarks with the view of 

 throwing light upon the more popular aspect of the 

 question — the processes of Analytic Heterogenesis. 



We have previously endeavoured to show that all the 

 processes or functions carried on in animal bodies are 

 effected at the cost of organic materials which are 

 assimilated in the form of Food -. These complex pro- 

 ducts are decomposed, so that ^ forces ' are liberated as 

 molecular movements ; this liberated molecular motion 

 communicates itself to the elements of the tissues and 

 organs, and supplies the motive power by which those 

 functions are carried on which gp to constitute vital 

 activity. It may reveal itself, for instance, in a display 

 of muscular or nervous power, whereby the organism 

 responds to impressions made upon it from without j or 

 ^ See vol. i. p. 423. 2 ^Jq\ j pp 23-49. 



