106 STORRS AGRICULTURAL EXPERIMENT STATION. 
only reduced the percentage of acid producing organisms, but 
apparently even retarded the increase in the actual numbers, 
Possibly the fact that they were strongly alkaline in their action 
upon media may have had a checking influence upon the acid 
species. However, the lactic acid species finally gained the 
ascendency, so that when plated at the end of three days they 
constituted by far the larger part of all the organisms present. 
The results of the experiments thus far conducted on this 
subject point quite conclusively to the following: 
1. Milk produced under ordinary conditions becomes con- 
taminated with considerable, frequently very large, numbers of 
bacteria. These organisms come from various sources, and 
comprise a large number of species. 
2. Many of the species gaining access to the milk find the 
conditions so different from their natural habitat that they are 
not able to multiply, and therefore they drop out very soon. 
Others which find the conditions not quite so unfavorable can 
multiply slowly for a time, but, gradually losing their vitality, 
disappear. 
3. Other species which gain access to the milk find the 
conditions well suited to their development, and multiply more 
or less rapidly and continuously from the very start. The 
lactic acid species, Bact. lactis acidi and B. lactis aerogenes, to- 
gether with certain non-acid species, come within this group. 
4. The decrease in the numbers of bacteria during the first 
few hours is not the result of any ‘‘ germicidal condition or 
property’’ possessed by the milk, but simply of the natural 
dropping out of those species which do not find the milk a suit- 
able medium in which to develop. 
5. When fresh milk contains the typical lactic organisms, 
namely Bact. lactis acidt and B. lactis aerogenes, even in very 
small numbers, they may be expected to increase continuously 
from the very outset. Immediate cooling is therefore necessary 
if the growth of these species is to be checked. 
6. Numerous other acid species which get into fresh milk 
do not find it well suited to their development, and disappear 
more or less completely during the ripening period. 
