THE THERMAL DEATH POINT OF BACTERIA I01 
EXERCISE XLII 
DETERMINING THE THERMAL DEATH POINT OF 
BACTERIA 
155. It is important to know the minimum temperature 
which will kill bacteria, especially the pathogenic forms. The 
uses to which such knowledge can be put are numerous in 
practical sanitary medicine, in disinfection, and in pasteuri- 
zation. For the various methods employed in making these 
determinations, see text-books and special articles on this sub- 
ject. The method here given, which can be followed by a full 
section of students, will give only approximate results. It 
should not vary, however, more than one degree from the 
actual thermal death point in moist heat of the organisms 
tested. In this exercise students may work in groups with 
satisfactory results and with the saving of much media. 
156. Work for this exercise. Take 10 tubes of bouillon ; 
place 8 of them in a wire basket and stand it in the thermo- 
“ regulated water bath.at 60°C. After 15 minutes remove the 
tubes and inoculate 4 of them from a culture of B. subihis 
and 4 of them from a culture of B. suipestifer or B. coli (the 
cultures will be furnished). In inoculating the tubes be sure 
not to touch the sides above the surface of the bouillon with 
the wire. 
After the tubes are inoculated return them to the water bath 
adjusted at 60°C. The water should come just above the 
liquid in the tubes. Remove the tubes, one of each species, 
as follows: one in 5 minutes, one in ro minutes, one in 15 
minutes, and one in 20 minutes. Label and place them in 
the incubator. 
Inoculate the other two tubes of bouillon, one from each of 
the cultures used, and place them in the incubator for controls. 
