SO-CALLED GERMICIDAL PROPERTY OF MILK. 93 
In order to get some data in regard to these problems, the 
experiments discussed in this article were undertaken by this 
Station. | 
METHOD USED IN THESE EXPERIMENTS. 
The results considered in these experiments were obtained 
from the mixed milk of a herd of about thirty cows. It was 
believed that results which might be obtained from mixed milk 
would be of greater practical value than results obtained from 
milk of individual cows, since the mixed milk would contain 
such organisms as are normally found in ordinary milk, while 
the milk from individual cows would be more or less influenced 
by the species which happen to exist in the udder of the par- 
ticular cow whose milk was used. 
As soon as the milk was drawn it was taken to the dairy 
room and cooled to a temperature of from 35°—40°F., and por- 
tions of this cooled milk were then taken to the laboratory for 
experimentation. A series of plate cultures was made imme- 
diately from these cooled samples, the culture media being the 
milk sugar litmus gelatin which has previously been described 
by this Station. As soon as the first series of plates was made, 
the milk was warmed up to 20°C. and held at that temperature 
until the end of the experiment. This temperature of 20° was 
chosen as being the most promising of results, since Hunziker 
found that at this temperature the so-called ‘‘germicidal ac- 
tion’’ was most pronounced. At the end of three hours a 
second series of plates was made from the sample; at the end 
of six hours a third series, and likewise at the end of nine 
and twelve hours. In a few experiments the samples were 
plated at intervals of two hours, but the results obtained did 
not differ in any noticeable degree from those obtained by 
plating every three hours. 
In every case six plates were made, using three different 
dilutions, and the figures given in these results are in each in- 
stance the averages of the six plates, so that errors of sampling 
and manipulation, so difficult to keep out of such work are 
largely eliminated, and the figures given represent quite accu- 
rately the condition of the milk at the time the test was made. 
The gelatin plates were incubated at a uniform temperature of 
BO.0 sau were, in most cases, not finally studied until they 
