COSMIC PHILOSOPHY 



half-century has wrought in the theories of life 

 with which Redi's doctrine has hitherto been 

 implicated. The hypothesis of a " vital prin- 

 ciple " is now as completely discarded as the 

 hypothesis of phlogiston in chemistry, or as the 

 Ptolemaic theory in astronomy : no biologist 

 with a reputation to lose would for a moment 

 think of defending it. The great discoveries 

 concerning the sources of terrestrial energy, illus- 

 trated in the foregoing chapter, have made it 

 henceforth impossible for us to regard the dy- 

 namic phenomena manifested by living bodies 

 otherwise than as resulting from the manifold 

 compounding of the molecular forces with which 

 their ultimate chemical constituents are endowed. 

 Henceforth the difference between a living and 

 a not-living body is seen to be a difference of 

 degree, not of kind, — a difference dependent 

 solely on the far greater molecular complexity 

 of the former. As water has properties that 

 belong not to the gases which compose it, so 

 protoplasm has properties that do not belong 

 to the inferior compounds of which it is made 

 up. The crystal of quartz has a shape which is 

 the resultant of the mutual attractions and re- 

 pulsions of its molecules ; and the dog has a 

 shape which is ultimately to be explained in the 

 same way, save that in this case the process has 

 been immeasurably more complex and indirect. 

 Such, in brief, is the theory by which the vital* 

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