SO-CALLED GERMICIDAL PROPERTY OF MILK. 99 
fact will be explained in the more detailed discussion of indi- 
vidual experiments later. Our experiments thus far have, in 
the more essential points, verified the points given by previous 
investigators on this question, and it is not our purpose in this 
paper to discuss the question of the decrease of bacteria in milk 
during the first few hours after leaving the cow. There can 
be but little question that such a decrease is the normal occur- 
rence in ordinary milk. ‘The purpose of these experiments is 
rather to investigate the cawse of this phenomenon, and the 
results certainly throw considerable light upon the subject. 
A study of the species found in the experiments made thus 
far enables us easily to divide them into three general groups 
according to the way in which the various species behave them- 
selves. ‘Ihe first group includes those experiments in which 
there was a decided reduction in the total number of bacteria 
during the first few hours, but at the same time a continuous 
increase in the acid producing bacteria from the very first, both 
in actual numbers and in percentage. In the second group are 
placed those experiments in which there was a more or less 
marked reduction in the total number of bacteria and also a 
reduction in the number of acid producing organisms during 
the first few hours until the minimum was reached, after which 
both the acid and non-acid producing species increased more 
or less rapidly. In the third group are included those results 
which showed a reduction in the total number of bacteria in 
the first few hours, accompanied by a continuous increase in 
the number of acid producing species, but at the same time a 
decrease in the percentage of the acid organisms. 
DISCUSSION OF GROUP I. 
The experiments of the type included in Group I. may be 
illustrated by the following tables representing two individual 
experiments. 
Table 31 shows that there was a decrease in the total number 
of organisms in the first few hours. The fresh milk contained 
12,550 bacteria, while at the end of three hours there were 
12,250, showing a decrease of 300 organisms, or 2.4 per cent. 
In the fresh milk there were 1,250 of the acid producing spe- 
cies, or 10 per cent. of the organisms present. At the end of 
three hours the milk contained 2,000 acid producing bacteria 
