BACTERIAL CONTAMINATION OF NORMAL MILK. 4! 



apparently inhabit the milk ducts. Indeed, in the majority 

 of cases where the subject has been carefully tested there 

 appear to be no typical lactic organisms in the milk while in 

 the duct. Milk drawn directly from the duct contains bacteria, 

 but in most cases contains bacteria incapable of souring and 

 curdling milk. In no experiment thus far recorded have 

 the common lactic bacteria, Bacterium lactis acidi (see p. 

 66), been found under conditions which indicate that they 

 come directly from the milk duct. It is true that milk 

 drawn immediately from the milk duct sometimes contains 

 lactic organisms and will subsequently sour, but, so far as 

 experiments have thus far indicated, the bacteria found in 

 these cases, although they produce lactic acid, are not the 

 usual lactic bacteria which, in the majority of cases, cause 

 the souring of milk. 



From the facts given it .will be evident that a con- 

 tamination of milk by bacteria during the milking is quite 

 unavoidable. The bacteria that are in the milk ducts will 

 inevitably be .washed out into the milk vessel, and no means 

 that can be devised can protect the milk from them. The 

 contamination from these sources may be in a measure re- 

 duced by allowing the first few jets of milk drawn to run to 

 waste, inasmuch as the first few jets will contain a larger 

 number of bacteria than any subsequent portion of the milk. 

 This practice of rejecting the first few jets is quite common 

 and is of use in reducing the number of bacteria, but it 

 never gets rid of them all. In other words, the bacteria 

 contamination that comes from the milk ducts is absolutely 

 unavoidable in the common method of milking. The only 

 possibility of obtaining sterile milk from the- cow would be 

 to collect small quantities of the milk drawn at the close of 

 a milking. By this means, if sufficient care is taken, sterile 

 milk can actually be obtained. The contamination by these 

 bacteria has also, in some cases, been avoided by passing a 

 small sterile tube into the duct and forcing it up into the 



