INTRODUCTION 15 



can give out by radiation. In many ways it seemed 

 to be, as Pfltiger said, a "semi-living" thing. His 

 theory has not been accepted by physiologists gener- 

 ally on the ground that, however interesting and 

 suggestive, the evidence was insufficient. It thus 

 fell the victim of a dull conservatism which dismissed 

 what was not established as if it were not true, 

 instead of taking the more philosophic course of pro- 

 curing further evidence to decide whether it was really 

 true or false. 



It seemed most logical to think that if cyanogen is 

 a living thing it would grow and multiply in culture 

 media. Thus the experiment was tried whether, under 

 varying conditions, it could be made to do so or not. 

 The results did not afford evidence from which con- 

 clusions could be drawn, unless those conclusions 

 were purely negative, the difficulties in the experi- 

 ments will be pointed out elsewhere. 



The physical analogy, on the other hand, between 

 the instability of cyanogen and radium and the 

 amount of energy stored up in them, although differ- 

 ing in the order of magnitude, led us to observe 

 the results, if any, which radium could produce upon 

 the same culture media. The results in this case 

 were quite definite and distinctly positive. Their 

 properties and minute behaviour were therefore 

 studied with the closest care. 



These bodies resembled bacteria in their appear- 

 ance. They could grow, subdivide, and go through 

 that cyclic process which is so often regarded as the 

 criterion or the test of life. For after a while the 



