110 LOUIS PASTEUR 



higher plants and animals. Their species breed as 

 true as those of sheep or cattle. Their form may 

 vary in different parts of their life cycle, but we 

 often meet with profound changes of form in the 

 life history of highly organized creatures. So far 

 as our experience goes it corroborates the truth of 

 the dictum, "Omne vivum e vivo," — all life from 

 antecedent life. And not only this, but it may 

 be said that all life comes from antecedent life 

 of approximately the same kind. The establish- 

 ment of this doctrine for minute forms of life in 

 the sense that it holds true for higher forms is an 

 achievement of far-reaching importance in many 

 relations. Pasteur was early convinced of its truth. 

 He did more than any one else to establish it. And 

 this principle served him as a most valuable guide 

 in grappling with the problems with which he was 

 destined to be occupied during the remainder of 

 his life. 



