20 BACTERIOLOGY. 



infusion was then to be boiled in the flask thus prepared 

 and the mouth of the tube left open. The organisms 

 which now fall into the tube will be arrested by the drop 

 of water of condensation which collects at its lowest 

 angle, and none can enter the flask. 



Though from our present-day standpoint the results 

 of these investigations seem to be of a most convincing 

 nature, yet there existed at the time many who required 

 additional proof that " spontaneous generation " was not 

 the explanation for the mysterious appearance of these 

 minute living objects. The majority, if not all, of such 

 doubts were subsequently dissipated through the well- 

 known investigations of Tyndall upon the floating matters 

 of the air. In these studies he demonstrated by experi- 

 ments that the presence of living organisms in decom- 

 posing fluids was always 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 organisms. 



Throughout all the work bearing upon this subject, 

 from the time of Spallanzani to that of Tyndall, certain 

 irregularities were constantly appearing. It was found 

 that particular substances required to be heated for a 

 much longer time than was necessary to render other 

 substances free from living organisms, and even under 

 the most careful precautions decomposition would occa- 

 sionally appear. 



In 1762 Bonnet, who was deeply interested in this 

 subject, suggested, in reference to the results obtained 

 by Needham, the possibility of the existence of " germs, 

 or their eggs," which have the power to resist the tern- 



