58 



MANUAL OF.BACTERIOLOGY. 



space inclosed by the hood also serves as a steam-jacket and 

 helps to overcome fluctuations in temperature. A great im- 

 provement upon the ordinary Arnold sterilizer is the modifica- 

 tion of it devised by the Massachusetts Board of Health. 



In the use of this, or any form of steam sterilizer, the time is 

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

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



Fig. 13. — Steam sterilizer, Massachusetts Board of Health. 



is better, when the thermometer registers 100° C, if the ster- 

 ilizer be provided with a thermometer. With a large Arnold 

 sterilizer a temperature of 100° 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 

 are to be sterihzed allowance must be made for the time neces- 

 sary to bring the temperature in the middle of the mass to 

 100° C. 



