162 MICEOBES, FERMENTS, AND MOULDS. 



Sterilized Flasks. Pasteur has shown that air may 

 be deprived of all its germs by being passed through 

 a capillary tube, turned back upon itself. He takes 

 a glass flask and draws out its neck so as to form 

 a long tube, which is bent in different directions 

 (Fig. 76). The prolonged application of heat expels 

 the air contained in the flask, which is therefore 

 sterilized, and it is then allowed to cool slowly. A 



\ 



Fig. 76. Pasteur's flask, with bent tube, containing a culture liquid, sterilized. 



hot culture liquid may now be put into the flask. It 

 must be ascertained, by keeping the flask at a tem- 

 perature of 36 for several days, that the liquid is 

 completely sterilized. The culture flasks are thus 

 fitted to receive the air which is to be the object of 

 study, together with the spores contained in it. 



Culture liquids. There is a considerable variety 

 of culture liquids : Pasteur's mineral solution, infusion 

 of hay or turnips, neutral urine, chicken-broth, beef- 

 tea, etc. They should be plunged in a bath heated 

 to a temperature of 150 to 180, since some spores 



