250 The Thermal Death-point 



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 exactly as in the other case. 



