The Thermal Death-point 301 



possess the maximum resisting power. To determine the 

 percentage, it is necessary to know how many bacteria were 

 present in the tubes before exposure to the destructive 

 temperature. Approximately the same number can be 

 placed in each tube by adding the same measured quantity 

 of a fluid culture to each. 



In both of the procedures one must be careful that the 

 temperature of the fluid in the test-tube is identical with that 

 of the water in the bath. A sterile thermometer introduced 

 into an uninoculated tube exposed under conditions similar 

 to those of the experiment can be used as an index for the 

 others. 



Another method of accomplishing the same end is by the 

 use of Sternberg's bulbs. These are small glass bulbs blown 

 on one end of a glass tube, drawn out to a fine point at the 

 opposite end. If such a bulb be heated so that the air is 

 expanded and partly driven out, its open tube, dipped into 

 inoculated bouillon, will in cooling draw the fluid in, so as 

 to fill it one-third or one-half. A number of these tubes are 

 filled in this manner with a freshly inoculated culture medium 

 and then floated, tube upward, upon a water-bath whose 

 temperature is gradually elevated, the bulbs being removed 

 from time to time as the required temperatures are reached. 

 As the bulbs are already inoculated, all that is necessary is 

 to stand them aside for a day or two, and observe whether 

 or not the bacteria grow, determining the death-point ex- 

 actly as in the other case. 



