From Inorganic Matter to Life. 167 



it is equally in conflict with all knowledge of nature 

 to assume it to be possible, by inappreciable increments 

 of molecular motion added on through infinitesimal 

 stages, to turn it into life. The difference between 

 living bodies and inorganic matter cannot be obliter- 

 ated by such gradations of change. 



4. When the evolutionist has advanced from in- 

 organic matter to life, he has then to undertake the 

 task of accounting for the innumerable varieties of 

 kind which characterize the organic kingdom. From 

 the lowest vegetal and animal forms to the highest, 

 over the whole range of life, the varieties surpass the 

 power of thought. How have all these arisen, and 

 how are they perpetuated ? Mr. Spencer answers by 

 introducing the "physiological unit." This special 

 creation, fills so important a place in his doctrine 

 that we must examine it closely as to its origin 

 and nature. " Organisms," he says, " are built up of 

 certain highly-complex molecules, which we distin- 

 guished as physiological units each kind of organ- 

 ism being built up of physiological units peculiar to 

 itself." * 



* Biology, Vol. II., 178. 



