Contamination of Milk. 49 



Harrison 1 has recently traced an off- flavor in cheese 

 in a Canadian factory to an infection arising from the 

 water-supply. He found the same germ in both water 

 and cheese and by inoculating a culture into pasteurized 

 milk succeeded in producing the undesirable flavor. 

 Milk can easily be infected through using such water for 

 washing utensils. Some well waters containing iron in 

 solution are a source of trouble in factories on account 

 of the development of iron bacteria that cause the solu- 

 ble iron to be precipitated in the form of rusty flakes of 

 ferric oxid. 



In ice the majority of organisms (60-90%) are de- 

 stroyed, but enough remain, so that if ice is secured 

 from a highly polluted source, the living germ life in it 

 may be an element of danger. It is not considered ad- 

 visable to add ice directly to milk or cream, but as stor- 

 age vessels are indiscriminately used to contain either 

 ice or milk, the possibility of infection should be kept 

 in mind. 



54. Numbers of bacteria in milk. The germ con- 

 tent of milk varies so greatly that unless the conditions 

 are all known, it is impossible to foretell what may be 

 found therein. An examination of milk will often reveal 

 a difference in numbers, ranging from a few score of 

 germs to hundreds of millions per cc. The presence of 

 such a varying number is dependent upon certain factors, 

 as the age of the milk, the care taken during the milking, 

 and also the way in which it has been handled since that 

 time. Disregarding milk of different ages, the number 

 of germs present in any sample bears a general relation 

 to the amount of dirt and filth with which it has come in 

 contact since it was drawn from the cow. Bacteria and 



1 Harrison, Hoard's Dairyman, Mch. 4, 1898. 

 4-B. 



