IXTliODUCTION. 19 



In 1836 Sehulz attracted attention to the subject by 

 the convincing nature of his investigations. He showed 

 that if the air which gained access to boiled infusions 

 was robbed of its living organisms by being caused to 

 pass through strong acid or alkaline solutions, no de- 

 composition appeared and living organisms could not 

 be detected in the infusions. Following quickly upon 

 this contribution came Schwann, in 1837, and somewhat 

 later (1854) Schroder and Dusch, with similar results ob- 

 tained by somewhat different means. Schwann deprived 

 the air which passed to his infusions of its living particles 

 by passing it through highly-heated tubes; whereas 

 Schroder and Dusch, by means of cotton- wool interposed 

 between the boiled infusion and the outside air, robbed 

 the air passing to the infusions of its organisms by the 

 simple process of filtration. In 1860 Hoffmann and in 

 1861 Chevreul and Pasteur demonstrated that the pre- 

 cautions taken by the preceding investigators for ren- 

 dering the air which entered these flasks free from 

 bacteria were not necessary ; that all that was necessary 

 to prevent the access of bacteria to the infusions 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 inches 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 fall into the 

 tube will be arrested by the drop of water of condensa- 

 tion which collects at its lowest angle, and none can 

 enter the flask. 



Convincing though this work may seem, there still 

 existed a number of doubters who required further proof 

 that " spontaneous generation " was not the explanation 



