160 



BACTERIOLOGY. 



dicated is of the author's own construction (see Fig. 37). As a rule,, 

 a regulator is not necessary when using the dry-heat sterilizer. 



FIG. 25. Dry-heat sterilizer, double width. In the corners, perforated brass 

 tubes to protect the thermometer and the thermoregulator. 



The time necessary to effect sterilization in the dry- 

 heat oven will, of course, depend upon the temperature. 

 The ordinary laboratory articles are quickly sterilized at 

 150. When the thermometer indicates 150, the time 

 should be noted, and this temperature should then be main- 

 tained for y?, to y^ of an hour. Glass tubes and dishes 

 are, therefore, to be sterilized in the dry-heat oven at a 

 temperature of 150-160 for ^-^ of an hour. A tem- 

 perature of 170, maintained for 15 minutes, will be suffi- 

 cient to effect sterilization. Another procedure is to allow 

 the temperature to rise till it reaches 195, when the light 

 is turned out. The door of the oven remains closed until 

 the temperature falls below 100. The cotton plug's in the 



