66 



MANUAL OF BACTERIOLOGY. 



quite effective. The space enclosed by the hood also serves 

 as a steam-jacket and helps to overcome fluctuations in tem- 

 perature. A great improvement upon the ordinary Arnold 

 sterilizer is the modification of it devised by the Massachu- 

 setts Board of Health. 



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

 time when sterilization is supposed to begin must be counted 



FIG. 14. 



Koch's Steam Sterilizer. 



as that when boiling is brisk and it is evident that the ster- 

 ilizing chamber is filled with hot steam; or, what is better, 

 when the thermometer registers 100 C, if the sterilizer be 

 provided with a thermometer. With a large Arnold ster- 

 ilizer a temperature of 100 C. may not be reached until it 



