4 Bacteria in Relation to Country Life 



ueous generation was not, however, implicitly accepted 

 by all. Bonnet pointed out the possible existence of 

 organisms, or their modifications, capable of withstand- 

 ing boiling temperatures, and even suggested that 

 Needham's flasks may have been improperly protected 

 against the entrance of bacteria from without. 



Spontaneous generation disproved. — In 1765 it was 

 demonstrated by Spallanzani that the development of 

 microorganisms in Needham's broth resulted from im- 

 perfect sterilization. By boiling the broth in the flask 

 for a long time, both the container and the contents 

 were thoroughly sterilized and no bacterial develop- 

 ment occurred. But, not content with this -proof, the 

 believers in spontaneous generation now maintained 

 that the liquid and the air above it had been so changed 

 by heating as to preclude the formation of microorgan- 

 isms. It was not difficult, of course, to demonstrate 

 that the liquid itself had not lost the power of under- 

 going putrefaction. It was merely necessary to open 

 the flask to the air in order to induce the appearance 

 and development of bacteria in the liquid. The com- 

 position of the atmosphere was still unknown at that 

 time, and no direct proof could, therefore, be adduced 

 in this connection. 



The matter thus rested, undecided, for several 

 decades, when Schultze brought forward the proof in 

 1836 that it is not necessary to heat the air in order to 

 deprive it of the microorganisms suspended in it. He 

 proved that this could also be done by passing the air 

 through strong acid or alkahne solutions. Schwann 

 secured similar results in the following year by forcing 



