24 BACTERIOLOGY 



investigations seem to be of a most convincing nature, yet 

 there were many at the time who required additional proof 

 that "spontaneous generation" was not the explanation 

 for the mysterious appearance of these minute living crea- 

 tures. The majority, if not all, of such doubts were sub- 

 sequently dissipated through the well-known investigations 

 of Tyndall upon the floating matters of the air. In these 

 studies he demonstrated by numerous ingenious and instruc- 

 tive experiments that the presence of living organisms in 

 decomposing fluids was ahvays to be explained either by 

 the pre-existence of similar living forms in the infusion 

 or upon the walls of the vessel containing it, or by the 

 infusion having been exposed to air which had not been 

 deprived of its viable organisms. 



Throughout all the work bearing upon this subject, from 

 the time of Spallanzani to that of Tyndall, certain irregu- 

 larities were constantly appearing. It was found that par- 

 ticular substances required to be heated for a much longer 

 time than was needed to render other substances free from 

 living organisms, and even after heating under the most 

 careful precautions decomposition would occasionally occur. 



In 1762 Bonnet, who was deeply interested in this sub- 

 ject, suggested, in reference to the results obtained by 

 Needham, the possibility of the existence of "germs or 

 their eggs," which had the power to resist the temperature 

 to which some of the infusions employed in Needham's 

 experiments had been subjected. 



More than a hundred years after Bonnet had indulged 

 in this pure speculation it became the happy privilege of 

 Ferdinand Cohn, of Breslau, to demonstrate its accuracy 

 and importance. 



Cohn repeated the foregoing experiments with like results. 



