54 



MANUAL OF BACTERIOLOGY. 



noted from the period when boiling is brisk and it is evident 

 that the sterilizing chamber is filled with hot steam; or, what 

 is better, when the thermometer registers ioo° C, if the ster- 

 ilizer be provided with a thermometer. With a large Arnold 

 steriHzer a temperature of ioo° C. may not be reached until it 

 has been heated with a rose-burner for twenty to thirty-five 

 minutes. When bulky articles or large amounts of material 



Fig. 14. — Koch's Steam Sterilizer. 



are to be sterihzed allowance must be made for the time 

 necessary to bring the temperature in the middle of the mass 

 to 100° C. 



The steriHzer invented by Koch is still largely in use. It is 

 a tall, cylindrical, tin vessel covered with asbestos or felt. The 

 lower portion is filled with water; on the side is a water-gauge 

 indicating the height of the water, in order that one may ob- 



