STERILIZA TION B Y HE A T. 53 



for their value upon the presence of more or less 

 unstable organic compounds, the object aimed at in this 

 method is to destroy the organisms in the shortest 

 time and with the least amount of heat. It is accom- 

 plished by subjecting them to the elevated temperature at 

 a time when the bacteria are in the vegetating or growing 

 stage i. e.j the stage at which they are most susceptible 

 to detrimental agencies. In order to accomplish this it 

 is necessary that there should exist conditions of tem- 

 perature, nutrition, and moisture which favor the vege- 

 tation of the bacilli and the germination of any spores 

 that may be present. When, as in freshly prepared 

 nutrient media, these surroundings are found, the spore- 

 forming organisms are not only less likely to enter the 

 spore stage than when their environments are less favor- 

 able to their vegetation, but spores which may already 

 exist develop very quickly into mature cells, 



It is plain, then, that with the first application of the 

 steam to the substance to be sterilized the mature vege- 

 tative forms of these organisms are destroyed, while cer- 

 tain spores that might have been present resist this 

 treatment, providing the sterilization has not been con- 

 tinued for too long a time. If now the sterilization is 

 discontinued, and the material which presents conditions 

 favorable to the germination of the spores is allowed to 

 stand for a time, usually for about twenty-four hours, 

 at a temperature of from 20-30 C., those spores which 

 resisted the action of the steam will, in the course of this 

 interval, germinate into the less resistant vegetative cells. 

 A second short exposure to the steam kills these forms 

 in turn, and by a repetition of this process all organisms 

 which were present may be destroyed without the appli- 

 cation of the steam having been of long duration at any 



