INTRODUCTION. 21 



or spore stage in the course of their life history, and 

 when in this stage they are much less susceptible to the 

 deleterious action of high temperatures than when they 

 are growing as normal vegetative forms. With the 

 discovery of these more resistant spores, the doctrine of 

 spontaneous generation received its final blow. It was no 

 longer difficult to explain the irregularities in the fore- 

 going experiments, or was it any longer to be doubted that 

 putrefaction and fermentation were the result of bacterial 

 life and not the cause of it, and that these bacteria were 

 the oifspring from preexisting similar forms. In other 

 words, the law of Harvey, Omne vivum ex ovo, or its 

 modification, Omne vivum ex vivo, was shown to apply, 

 not only to the more highly organized members of the 

 animal and vegetable kingdoms, but to the most micro- 

 scopic, unicellular creatures as well. 



Note. — I have presented only the most prominent 

 investigations which aided in overthrowing the doctrine 

 of spontaneous generation. For a more detailed account 

 of this work the reader is referred to Loffler's Vorle- 

 sungen uher die geschichtliohe JSntwiokelung der Lehre 

 von den Bacterien, upon which I have drawn largely in 

 preparing the foregoing sketch. 



2* 



