54 BACTERIOLOGY. 



fers, in two respects, viz., it requires a greater number 

 of exposures for its accomplishment, and the tempera- 

 ture at which it is conducted is not raised above 68°- 

 70° C. It is employed for the sterilization of easily 

 decomposable materials, which would be rendered use- 

 less, by the temperature of steam, but which remain 

 intact at the temperature employed. This process 

 requires that the material to be sterilized should be sub- 

 jected to a temperature of 68°-70° C. for one hour on 

 each of six successive days, the interval of twenty-four 

 hours between the exposures admitting of the germina- 

 tion of spores into mature cells. During this interval 

 the substances under treatment are kept at about 25°— 

 30° C. The temperature employed in this process 

 suffices to destroy the vitality of almost all organisms in 

 the vegetative stage in about one hour. Until recently 

 blood-serum was always sterilized by the intermittent 

 method at low temperature. 



Sterilization by steam is also practised by what may 

 be called the direct method. That is to say, both the 

 mature organisms and the spores which may be present 

 in the material to be sterilized are destroyed by a single 

 exposure to the steam. In this method steam at its 

 ordinary temperature and pressure — live steam or stream- 

 ing steam as it is called — is employed just as in the first 

 method described, but it is allowed to act for a much 

 longer time, usually not less than one hour ; or, steam 

 under pressure, and consequently of a higher tempera- 

 ture, is now frequently employed. In this method a 

 single exposure of fifteen minutes is sufficient for the 

 destruction of all bacilli and their spores, providing the 

 pressure of the steam is not less than one atmosphere 

 over and above that of normal — this is approximately 



