INTRODUCTION 9 



evolution of worlds, the theory of spontaneous genera- 

 tion seems to be the last resort to which to turn. 



In prescientific days this idea of spontaneous genera- 

 tion presented no great difficulties to our imaginative 

 and credulous ancestors. John Milton, with the assur- 

 ance of an eye-witness, thus described the inorganic 

 origin of a lion: 



"The grassy clods now calved; now half appears 

 The tawny liorr, pawing to get free 

 His hinder parts then springs as broke from bonds, 

 And rampant shakes his brindled mane." 



("Paradise Lost/' Book VII, line 543.) 



Ovid also in his "Metamorphoses," not to mention a 

 more familiar instance of special creation, easily suc- 

 ceeded in creating mankind from the humble stones 

 tossed by the juggling hands of Deucalion and Pyrrha. 



Although under former conditions on the earth 

 it might have been possible for life to have originated 

 spontaneously, and although it may yet be possible 

 to produce life from inorganic materials in the labora- 

 tory or elsewhere, the exhaustive work of Pasteur, 

 Tyndall and others effectually demonstrated a genera- 

 tion ago that to-day living matter always arises from 

 preceding living matter and this conclusion is gener- 

 ally accepted as an axiom in genetics. 



There are various methods of producing more life, 

 given a nest-egg of living substance with which to 

 start. Any organism, whether plant or animal, is 

 continually transforming inorganic and dead material 

 into living tissue. Through the process of repair, for 

 example, an injury to a form as highly developed 



