38 SOURCE OF BACTERIA IN MILK. 



onstrated by a direct examination of the gland itself. If the 

 glands of slaughtered animals are carefully cut open and the 

 contents of their milk ducts tested directly with all proper 

 bacteriological precautions, it is easy to demonstrate satis- 

 factorily the presence of bacteria in the ducts. 



Although bacteria are certainly present in the milk ducts 

 it is not at the present time positively kno.wn how far within 

 the gland they extend. That the bacteria come from an 

 external source, passing in through the milk teat and living 

 within the gland, is perfectly evident, but experiments hith- 

 erto reported are not in agreement as to the depth to which 

 the bacteria can penetrate into the glands. In some tests it 

 has appeared that bacteria may be found in all parts of the 

 gland, even in the small ducts in its upper portions. Other 

 experimenters have found that the milk in the upper ducts 

 of the milk gland is sterile, the ducts here containing no 

 bacteria, whereas the lower ducts near the cistern, and par- 

 ticularly below it, are always filled with bacteria (34). The 

 only conclusion we can reach at present is, therefore, that 

 bacteria are present in the milk cistern and extend for a 

 considerable distance above, and that they are present in 

 sufficient quantities to contaminate the milk during the milk- 

 ing, especially the first portion drawn at each milking. 



The bacteria .which are present in these ducts find here 

 their normal habitat, and live, grow and multiply here in a 

 perfectly normal fashion. This follows from the fact that, 

 although the ducts are quite thoroughly washed out at each 

 milking, so that the milk at the close is nearly sterile, bac- 

 teria are always present at the beginning of the next milk- 

 ing in considerable abundance, a fact which proves that they 

 must have multiplied during the interval between the milk- 

 ings. It is a curious fact, however, that it makes compara- 

 tively little difference whether the intervals between the 

 milkings are moderately short or very long (17). If the 

 interval between the milkings is as long as six hours the 



