q 
76 STORRS AGRICULTURAL EXPERIMENT STATION. 
Experiment No. 13.—This experiment was conducted pre- 
cisely similar to the previous one, with the exception that some 
of the tubes were placed in a more concealed place, where they 
were less likely to be directly contaminated with dirt. Three 
tubes of sterile milk were placed in a position where they were 
> well exposed to the air, and five were hidden behind a tall 
board near a window several feet from the cows, where little 
dust would be likely to reach them. After the tubes had been 
exposed 12 hours they were plugged with cotton and placed in 
the laboratory. ‘Those which had been most exposed to the 
dust became strongly acid and in 36 hours had curdled. These 
tubes were tested by the ordinary plate cultures and were found 
to contain all of the three acid varieties, including the B. aczdz 
lactici which was sought. ‘The tubes which had been hidden. 
behind a board, however, did not curdle before 72 hours, and 
plate cultures failed to show the presence of B. actdi lactict. 
They were, however, slightly acid and contained the two other 
species of lactic bacteria. 
Experiment No. r4.—Sterile milk tubes were exposed in the 
open stable for 12 hours and then plugged and brought to the 
laboratory, as in the previous experiments. All tubes curdled 
and became acid. ‘They were tested with plate cultures in the 
ordinary way and large numbers of each of the three species of 
lactic bacteria were found in them. 
Experiment No. 15.—A final test was made as follows: Tubes 
of sterile milk were exposed for about 20 minutes underneath 
several of the cows during the process of milking. At the same 
time samples of milk from each cow were drawn directly into 
sterile vials and plugged at once. In this way stevzle milk was 
exposed to external contamination, while the fresh milk was 
drawn in such a way as to prevent external contamination. 
The samples of milk which were drawn directly into sterile 
vials failed to curdle and contained no acid organisms, as in all 
the previous experiments. On the other hand, the tubes of 
sterile milk which had been exposed under the cows’ flanks 
for 20 minutes all curdled, and each showed the presence of 
all three species of lactic bacteria. 
