312 APPLICATION OF METHODS OF BACTERIOLOGY 



action of steam for two minutes; then place it to one side 

 for from twenty to twenty-four hours, and again heat for 

 two minutes; allow it to stand for another twenty-four 

 hours, and repeat the process on the third day. No pellicle 

 will be formed, and yet spores were present in the origmal 

 mixture, and, as we have seen, the spores of this organism 

 are not killed by an exposure of five minutes to steam. How 

 can this result be accounted for? 



Saturate several pieces of cotton thread, each about 2 cm. 

 long, in the original decomposed bouillon, and dry them 

 carefully at the ordinary temperature of the room; then at 

 a little higher temperature — about 40° C. — to complete 

 the process. Regulate the temperature of the hot-air 

 sterilizer for about 100° C, and subject several pieces of 

 this infected and dried thread to this temperature for the 

 same lengths of time that we exposed the same organisms 

 in bouillon to the steam, viz., five, ten, thirty, and sixty 

 minutes. At the end of each of these periods remove a bit 

 of thread, and prepare a set of plates or Esmarch tubes 

 from it. Are the results analogous to those obtained when 

 steam was employed? 



Increase the temperature of the dry sterilizer and repeat 

 the process. Determine the temperature and time neces- 

 sary for the destruction of these organisms by dry heat. 

 These threads should not be simply laid upon the bottom 

 of the sterilizer, but should be suspended from a glass rod, 

 which may be placed inside the oven, extending across its 

 top from side to side. 



Place several of the infected threads in the centre of a 

 bundle of rags. Subject this to a temperature necessary to 

 sterilize the threads by the dry method. Treat another 

 similar bundle to sterilization by steam. In what way do 

 the results of the two processes differ? 



