72 BACTERIOLOGY. 



other hand, if the vessels be nearly filled with media, 

 and especially if the area of the surface be small, the 

 conditions are much more favorable to the germination 

 of anaerobic spores, and sterilization by this process after 

 such precautions is usually perfect. 



Fortunately, these undesirable experiences are rare, 

 but that they do occur, and result in no small degree 

 of annoyance, will be admitted by most bacteriologists. 



It must be borne in mind that this method of steril- 

 ization is only applicable in those cases which present 

 conditions favorable to the germination of the spores 

 into mature vegetative cells. Dry substances, such as 

 instruments, bandages, apparatus, etc., or organic ma- 

 terials in which decomposition is far advanced, where 

 conditions of nutrition favorable to the germination of 

 spores are not present, do not offer the conditions requi- 

 site for the successful operation of the principles under- 

 lying the intermittent method of sterilization. 



FRACTIONAL STERILIZATION. The process of frac- 

 tional sterilization at low temperatures is based upon ex- 

 actly the same principle, but differs in two respects from 

 the foregoing in the manner by which it is practised, viz., 

 it requires a greater number of exposures for its accom- 

 plishment, and the temperature at which it is conducted is 

 not above 68-70 C. It is employed for the sterilization 

 of easily decomposable materials, which would be rendered 

 useless by steam, but which are unaltered by the tem- 

 perature employed, and for certain albuminous culture- 

 media that it is desirable to retain in a fluid condition 

 during sterilization, but which would be coagulated if 

 exposed to higher temperatures. This process requires 

 that the material to be sterilized should be subjected to 



