40 THE MICROSCOPE. Mar. 



pared in the Royal Institution in London. He covered 

 the substance from which the infusion was to be made, 

 with distilled water kept at a temperature of 120° Fahr. 

 After digesting the substance for four or five hours, he 

 poured oS the liquid, boiled it, filtered it and obtained a 

 clear infusion. The liquid was then cooled and its spe- 

 cific gravity found. The flasks used were similar to that 

 shown in Figure 1. These were filled by placing the 

 tube in the infusion, heating the flask and then chilling 

 it. The air within then condenses and is followed by the 

 infusion. The flasks were then plunged in the boiling 

 oil for five minutes, the steam escaping by the open neck. 

 While the steam was still escaping a Bunson flame was 

 applied to the neck and sealed it by melting the glass. 

 The flask is then drawn from the oil perfectly sealed 

 hermetically. Aster arriving at the Alps, 54 of the 60 

 flasks were found to be clear, the other 6 muddy but 

 these on being carefully examined were each one found 

 to have the nip of the neck broken off and hence admit- 

 ted some air. The infusion in the muddy flasks was 

 found to be crowded with life but which could not have 

 been the result of spontaneous generation; or, if so, how 

 account for the clearness of the 54 ? The fact that air 

 was admitted into the 6 muddy ones and that these alone 

 showed life tends to show if it does not prove that in 

 this case ordinary air was necessary to the production of 

 bacteria. But to prove that it is not the air itself, but 

 something present in the air which produced the life, 

 Tyndall went further. He divided the 54 clear flasks 

 into groups of 23 and 27 ; the 23 he carried into a hay 

 loft and broke off the ends of the necks admitting air. 

 He then carried the 27 to a greater elevation in pure air 

 and taking precautions lest any dust from his clothing 

 or from the nippers should enter the flasks he nipped off 

 the ends of the 27. He then placed the 50 flasks over a 

 kitchen stove in a temperature varying from 50° to 90° 



