56 BACTERIOLOGY. 



in a fluid condition during sterilization, but which would 

 be coagulated if exposed to high temperatures. This 

 process requires that the material to be sterilized should 

 be subjected 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 germination 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. By the latter pro- 

 cedure a single exposure of fifteen minutes is sufficient 

 for the destruction of practically 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 equivalent to a temperature of 

 122 C. to which the organisms are exposed. 



The objection that has been urged to both of these 

 methods, particularly that in which steam under press- 

 ure is employed, is that the constitution of the media is 



