302 BRIEF HISTORY OF BACTERIOLOGY UP TO 1881 



the first experiment in which the principle of ''dry heaf or 

 ''hot air" steriHzation was used. Similar arguments were 

 brought forward, also to the use of cotton ylugs as filters, by 

 Schroeder and Dusch in 1859 (Fig. 173). This was the first 

 use of the principle of sterilization hy filtration. It remained 

 for Chevreuil and Pasteur to overcome this objection in 

 1861 by the use of flasks with long necks drawn out to a 

 point and bent over. These permitted a full access of air 

 by diffusion but kept out living germs, since these cannot 

 fly but are carried mechanically by air currents or fall of 

 their own weight (Fig. 174) . Hoffman, theyearbefore (1860), 

 had made similar experiments but these remained unnoticed. 

 The Pasteur flasks convinced most scientists that "spon- 

 taneous generation" has never been observed by man, 

 though some few, notably Dr. Charlton Bastian, of England, 

 vigorously supported the theory from the early seventies 

 until his death in November, 1915. 



Fig. 174.— Pasteur's flask. 



John Tyndall, in combating Bastian's views, showed that 

 boiled infusions left open to the air in a closed box, through 

 which air circulated, did not show any growth of organisms 

 provided the air was so free of particles that the path of a 

 ray of light sent through it from side to side could not be 

 seen (Fig. 175). Or if such sterilized infusions were exposed 

 to dust-free air, as in the high Alps, the majority showed no 

 growth, while all infusions in dusty air did show an abun- 

 dance of organisms. Tyndall's experiments confirmed those 

 of Pasteur and his predecessors and showed that the organ- 



