104 LABORATORY BACTERIOLOGY 
to go to the bottom of the inoculated tube. Label each with 
the strength of the disinfectant and time of exposure and 
place it in the incubator. It should be noted that the add- 
ing of .25 cc. of culture diluted slightly the strength of the 
disinfectant. 
Note at the next exercise the condition of each inoculated 
tube. From them the approximate strength of the disinfectant 
used and the time necessary to destroy the bacteria can be 
determined. When this is found the more exact strength and » 
time can be determined by repeating the experiment with 
weaker dilutions or shorter exposures or both. 
Examine cultures that were heated at the previous exercise. 
