CLASSIFICATION OF DAIRY BACTERIA. 23 
conclusion has not been borne out by the direct studies of bac- 
teria in the milk ducts. Our recent experiments seem rather 
to point to the conclusion that this organism comes from exter- 
nal contaminations. When we have collected samples from 
large numbers of cows, drawing the milk directly from the 
teats into sterilized vessels with little or no chance for contam- 
ination, it has been found that milk thus obtained only in very 
rare cases contains the organism No. 206. In the experi- 
ments, which now number over 200 and involve 75 well kept 
cows, there have been only five instances where such milk 
contained this organism, and the cows concerned in these five 
cases did not show the same result with a second test. The 
milk obtained directly from the cows in this way contained many 
species, commonly including liquefying bacteria, but not this 
common lactic species. When, however, the milk is drawn 
from the cow into sterilized vessels with a more widely open 
mouth, the organism in question has been found in most cases 
to be present, and becomes abundant in a few hours. ‘This 
indicates that the &. aczdit lactict should be regarded as an 
organism which comes from external contamination, and is 
not a normal inhabitant of the milk duct. On the other hand, 
up to the present time I have not succeeded in finding the 
organism in question present in any considerable numbers in 
gelatin plates which have been exposed to the air underneath 
the cow during the milking process. My present belief is that 
this organism is not a normal inhabitant of the milk duct, but 
commonly is derived from external sources, and is practically 
always present in the milk vessels into which the milk is drawn. 
Next in abundance to the organism just described is No. 
“202. This may perhaps be a variety of the last, but it differs 
from it in being more markedly anaerobic, and in producing a 
colony in gelatin which is extremely minute and indeed invis- 
ible to the naked eye, whereas No. 206 produces a good sized 
colony. This is also very abundant in nearly all samples of 
sour milk or cream, although the numbers are much less than 
those of the last species. This organism I have not been 
able to find in the milk ducts any more than the last, and I 
regard it also as being derived from external contamination. 
These two species undoubtedly belong together, not only 
from their morphological similarity and their general likeness 
