SOURCES OF POLLUTION 181 



discoveriug." * Subsequent experiment has only confirmed the 

 general truth of this statement.! With efficient precautions it is 

 possible to draw from the udder of a healthy cow perfectly sterile 

 milk, which retains its sterility unchanged for long periods of time 

 in a sterilised and sealed flask. Yet we know by practical experi- 

 ence as well as by ultimate changes in the milk, that, generally 

 speaking, the presence therein of bacteria is very marked. 



Sources of Pollution of Milk 



These are various, and depend upon many minor circumstances 

 and conditions. For all practical purposes there are four chief 

 opportunities between the cow and the consumer when milk may 

 become contaminated with bacteria: — 



1. At the time of milking and during manipulation at the farm. 



2. During transit to the town, or dairy, or consumer. 



3. At the milkshop. 



4. In the home of the consumer. 



Pollution at the time of milking arises from the animal, the 

 milker, or unclean methods of milking. It is now well known that 

 in tuberculosis of the cow affecting the udder the milk itself shows 

 the presence of the bacillus of tubercle. In a precisely similar 

 manner all bacterial diseases of the cow which affect the milk- 

 secreting apparatus must inevitably add their quota of bacteria to 

 the mUk. To this matter we shall have occasion to refer again. 

 There is a further contamination from the animal when it is kept 

 unclean, for it happens that the unclean coat of a cow will more 

 materially influence the number of micro-organisms in the milk than 

 the popularly supposed fermenting food which the animal may eat. 

 It is from this external source rather than from the diet that 

 organisms occur in the milk. The hairy coat offers many facilities 

 for harbouring dust and dirt. The mud and filth of every kind that 

 may be habitually seen on Lhe hinder quarters of cattle all contribute 

 largely to polluted milk. Nor is this surprising. Such filth at or 

 near the temperature of the blood is an almost perfect environment 

 for many of the putrefactive bacteria. 



The milker is also a source of risk. His hands, as well as the 

 clothes he is wearing, can and do readily convey both innocent and 

 pathogenic germs to the milk. Clothed in dust-laden garments, and 

 frequently characterised by dirty hands, the milker may easily act 

 as an excellent purveyor of germs. Not a few cases are also on 

 record where it appears that milkers have conveyed germs of 



* Transaetions of Pathological Society of London, 1878, p. 440. 

 f See also Rotch, Pediatrics, the Hygiene and Medical Treatment of Children, 

 London, 1896. 



