266 WHAT IS LIFE 



or corroborative value, of this agreement between 

 demand of theory concerning neoplasms and the 

 phenomena of cancer — the phenomena of both the 

 abnormal "proliferation" of cells, as which (for want 

 of a closer definition) cancer has been described by 

 some pathologists, and of those cancers which, 

 according to some researchers of unquestioned 

 ability, show the presence of minute organisms. 



Thus it would appear that while the theory states 

 the cause of cancer, the phenomena of cancer con- 

 stitute a striking proof of the theory. 



Another demand of theory concerns specificity of 

 species. This demand of theory is met by the fact 

 that "species" appear to be constant. {See Chapter 

 Seven.) 



The theory makes several demands of geology. 

 (See Chapter Seven.) The easy harmony that is 

 found to obtain between these demands and the 

 pertinent facts of the geologic record, not improperly 

 may be said to be in the nature of proof of the correct- 

 ness of the theory. 



The theory then, plainly, is well supported. Yet 

 there remains the imperative demand for direct ex- 

 perimental proof. This is simply because to the 

 trained, critical mind, absolute conviction in matters 

 of science which may be referred to the laboratory 

 can come only through positive and conclusive proof 



