20 SA CTEBIOL OGY. 



sions in the flasks was to draw out the neck of the flask 

 into a fine tube, bend it down along the side of the 

 flask, and then bend it up again a few centimetres from 

 its extremity, and leave the mouth open. The infusion 

 was then to be boiled in the flask thus prepared and the 

 mouth of the tube left open. The organisms which 

 now fell into the open end of the tube were arrested l)y 

 the drop of water of condensation which collected at its 

 lowest angle, and none could 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 mat- 

 ters of the air. In these studies he demonstrated by 

 experiments that the presence of living organisms in 

 decomposing fluids was always to be explained either 

 by the pre-existenee of similar living forms in the infu- 

 sion 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 ajjpearing. 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 



