STERILIZATION 79 



Frisch, in 1877, exposed both bacilli and micrococci to minus 

 87 C, produced by the evaporation of liquid carbon dioxide. 

 All such bacteria grew when brought under favorable condi- 

 tions. 



A number of later experiments showed that while freezing 

 kills a certain number of the bacteria it does not kill all of 

 them by any means, and many forms -may remain alive for 

 months in frozen water. This is true also of disease-produc- 

 ing bacteria. 



Dry Heat. In 1854, Schultz and Schwann first showed 

 the real value of dry heat in destroying bacteria in their ex- 

 periments upon spontaneous generation (see Chap. II). 



Direct Flame. This is constantly used in the laboratory 

 for sterilizing the platinum needles, but its use is almost 

 entirely limited to this and to the destruction of worthless 

 but infectious material, such .. as the carcasses of infected 

 animals. In this case, a special apparatus is necessary, 

 known as the incinerator. 



High Dry Heat. Dry heat at a temperature of 150 C. 

 is constantly used in the laboratory for the sterilization of 

 such materials as glassware, cotton batting, etc. It has been 

 shown that this temperature is sufficient to kill all forms of 

 life, and may be depended upon as a means of producing per- 

 fect sterilization, providing the heat can readily reach all 

 parts of the objects to be sterilized. The heat is supplied in 

 an oven or a hot-air sterilizer. This is sometimes provided 

 with a thermometer, but usually this is not necessary, since 



