232 BACTERIOLOGY. 



scopic methods are deceptive ; cloudiness of the media 

 or the presence of organisms microscopically does not 

 always signify that the organisms possess the property 

 of life. 



Inoculate in the same way a third flask of bouillon 

 with a very small drop from one of the old cultures 

 upon which the pellicle has formed ; mix it well and 

 subject it to the 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 original mixture, and, as we have 

 seen, the spores of this organism are not killed by an 

 exposure of five minutes to the 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 tempera- 

 ture 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 anal- 

 ogous to those obtained when steam was employed ? 



Increase the temperature of the dry sterilizer and 

 repeat the process. Determine the temperature and 

 time necessary for the destruction of these organisms 



