68 BACTERIOLOGY. 



is reached where it is killed. The test is best carried 

 out by means of small glass bulbs, the so-called Stern- 

 berg bulbs, or through the use of capillary tubes con- 

 taining a small amount of fluid inoculated with the 

 organism to be studied. The bulb, or tube, is sealed in 

 the gas flame and placed in a water-bath kept at 50 C. 

 for five minutes. Sub-cultures are now made to learn 

 whether the bacteria have been killed or not. If the organ- 

 ism survives the test is repeated at 55, 60, 65, and 

 70 C. Finally, the test is repeated for each degree of 

 temperature between the points where growth is still 

 apparent and where the organisms have been killed. 

 If the bacteria were killed when heated to 60 C. for 

 five minutes, but survived when heated to 55 C., then 

 similar tests are made for the same length of time for 

 each degree of temperature between 55 and 60 C. It 

 will usually be found that heating for ten minutes suf- 

 fices to kill the bacteria at a temperature one or two de- 

 grees lower than that required when heated for only five 

 minutes. All such tests should be made at least in 

 duplicate, and the mean of the results taken. 



