TO DETERMINE THERMAL DEATH-POINT. 241 



removed as soon as it is certainly heated through, another 

 in five minutes, another in ten minutes, or at whatever 

 intervals the thought and experience of the experimenter 

 shall suggest. 



In both of the described procedures one must be care- 

 ful that the temperature in the test-tube is identical with 

 that of the water in the bath. There is no reason why a 

 sterile thermometer should not be placed in the heated 

 tube in the first case, and in the second experiment one 

 of the test-tubes exposed under conditions similar to the 

 others might contain a thermometer which would show 

 the temperature of the contents of the tube containing it, 

 and so be an index of the rest. 



Another method of accomplishing the same end is to 

 use Sternberg's bulbs. These are small glass bulbs 

 blown on one end of a piece of glass tubing, which is 

 subsequently drawn out to capillarity at the opposite end. 

 If such a bulb be heated, and its capillary tube dipped 

 into inoculated bouillon, in cooling, the fluid is drawn in 

 so as to fill it one-third or one-half. A number of these 

 tubes are filled in this manner with 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. Of course, 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, judging the death-point exactly 

 as in the other case. 



To Determine the Antiseptic and Germicidal Value 

 of Reagents. — There are various methods whose modi- 

 fications can be elaborated according to the extent and 

 thoroughness of the investigation to be made. 



I. The Antiseptic Value. — Remembering that an anti- 

 septic is a substance that inhibits bacterial growth, the 

 method that will at once suggest itself is that of adding 

 varying quantities of the antiseptic to be investigated to 

 culture-media in which the bacteria are subsequently 



16 



