CHANGES IN MILK 51 



VII. CHANGES IN MILK CAUSED BY 

 MICRO-ORGANISMS 



Milk found in the glandular passages and cisterns of 

 the healthy udder is usually sterile. On the other hand, 

 the ducts of the teats and, still more, the ends of the 

 teats usually contain bacteria and, therefore, the milk 

 when drawn is infected with them. This is more apt to 

 be the case when the milk comes in contact with the 

 hands of the milkers, or when it is poured into the not 

 always sterile bucket, or when particles of dirt and dust 

 from the udder or the skin of the cow, from the clothing 

 of the milkers or from the air, drop into the milk. 

 Before the milking is finished, a considerable number of 

 different bacteria have been added to the milk and 

 though, for a time, it has bactericidal properties, that 

 is, it is able to kill bacteria or, at least, to prevent their 

 growth, yet the number of bacteria does not diminish 

 noticeably but, in the course of time, increases enor- 

 mously. Shortly after milking, thousands, even hun- 

 dreds of thousands, of bacteria may be found in each 

 cubic centimetre. 



In inflammatory processes, catarrh, tuberculosis and 

 actinomycosis of the udder, infected wounds at the open- 

 ing of the teat, etc., bacteria are more or less numerous 

 in the milk before it is drawn. In benign udder inflam- 

 mations bacteria disappear almost entirely with the 

 cessation of the disease, but occasionally it happens that 

 the bacterial growth continues for a time in the milk 

 contained in the glandular passages, after the secretion 

 has become apparently quite normal and after all signs 

 of inflammation have disappeared. 



In general infections, not localized in the udder, as 

 a rule no microbes are excreted with the milk. An excep- 

 tion to this is foot-and-mouth disease (aphthous fever), 

 in which the milk of the affected cows often contains vir- 



