SPONTANEOUS GENERATION 



301 



but the "spontaneous generation" theorists raised the same 

 objection, i. e., the change in the air by heating. This was 



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Fig. 172.— Schwann's experiment. After boiling, as shown in the diagram, 

 and cooling, air was drawn into the flask by aspiration while the coiled tube 

 was kept hot with the flame. 



Fig. 173. — Schroeder and Dusch's experiment. The aspirating bottle drew 

 the air through the flask after it had been filtered by the cotton in the tube. 



