MICRO-ORGANISMS IN MILK 267 



sources of bacterial pollution during the journey of milk from the 

 cow to the consumer. A more detailed discussion of these sources 

 will be taken up under the following heads : 



1. Contamination in the udder. 



2. Contamination during milking operations. 



3. Contamination from utensils, machinery, bottles, etc. 



4. Contamination during transportation. 



5. Contamination in the hands of dealers and consumers. 



Contamination in the Udder 



Based on observations of Roberts, Lister, Htippe, and others 

 the belief was for some time prevalent that milk in the healthy 

 udder contained no micro-organisms. By using a sterile cannula 

 connected with a sterile flask milk has been obtained by these 

 observers that seemed to remain unchanged for long periods 

 unless exposed to the influence of the air. Lister in 1877 declared 

 that "unboiled milk, as coming from the healthy cow, really has 

 no ferment in it capable of leading to lactic fermentation or any 

 other fermentation or any organic development whatever." This 

 statement was based on an experience with two samples of milk. 

 TrommsdorfE claimed that he could easily obtain milk "absolutely 

 free from germs" in any quantity desired by introduction through 

 the teat duct of a catheter 10 cm. long and 1.5 mm. in diameter. 

 And Evans and Cope also worked with milk obtained by introduc- 

 tion into the udder of a cannula that was supposedly sterile. Swith- 

 inbank and Newman obtained sterile milk by a simple apparatus, 

 description of which is given in their book "The Bacteriology 

 of Milk." They think that "no great difficulty need be experi- 

 enced in obtaining sterile milk direct from the udder of the nor- 

 mally healthy cow." With the simple apparatus designed by 

 them "the authors have for some years past foimd no difficulty 

 in holding ready to hand a constant supply of sterile milk in its 

 natural condition." 



Later work, however, has shown that milk in the udder usually 

 contains micro-organisms, and that even the strippings are not 

 always sterile, although, as far as present knowledge goes, milk is 

 secreted in a sterile condition by healthy mammary glands. 



Schulz in 1892 examined milk at different stages of the milk- 

 ing process, and found that the first streams are richest in bac- 

 teria and that the number decreases as milking progresses. 

 Moore, agreeing with Schulz, states that it is an exception to find 

 milk directly from the udder free from micro-organisms, unless 

 taken during the latter part of the milking process from a single 

 quarter of the udder. 



