26 Microbes and You 



infusions, especially during the cooling stage when negative 

 pressure within the flasks tended to suck contaminated air into 

 the vessels. 



Spallanzani, exhibiting a truly scientific approach to the prob- 

 lem, tried to beat his own theory disproving spontaneous genera- 

 tion. His critics claimed that in boilino; his infusions for such a 

 long time, he had devitalized the substrate and organisms could 

 not grow. Spallanzani took some seeds which he had found to be 



Fig. 9. Lazzaro Spallanzani (1729-1799). {From Fundamentals 

 of Bacteriology, M. Frobisher, 4th. ed. Copyright 1949, W. B. Sound 

 ers Company, Fhiladelphia.) 



good food for microbes, and he roasted these seeds until they were 

 black— certainly devitalizing them, if such was the case. When he 

 added water to this charred medium, he found that access to air 

 soon provided the necessary germs which readily multiplied in his 

 seed infusion. This proof was finally accepted by most persons, 

 and he was proclaimed all over Europe, but a few persisted in 

 their denunciation of the man because they felt that sealing the 

 flasks had removed a vital force in air necessary for microbial 

 growth. 



To combat this criticism Franz Schultze (1836) passed air 

 through his infusions after forcing the air through caustic potash 



