1902 



Bacterial Contamination of Milk. 471 



Von Freudenreich,^^ on the other hand, states that when in the 

 udder milk is free from bacteria, except when the milk glands are in a 

 diseased condition. 



H. L. Bolley and C. M. Hall,^^ in their studies of the bacterial flora 

 of the milk of ten healthy cows, isolated sixteen distinct species of 

 bacteria, some of which were common to both the first and last milk, 

 and others to only one of these. All the micro-organisms found were 

 bacteria, and none were found which produced gas. 



RusselP in his text-book on Dairy Bacteriology, published in 1894 

 states that he has found an average of 2,800 germs per c.c. in the fore- 

 milk, while the average of the remainder of the milk only had 330 germs 

 per c.c. In characterizing this, he says that " the number of species is 

 usually small, one or two kinds usually predominating to a large 

 degree. Those that are commonly found are those that produce lactic 

 acid, as these microbes find in milk the best medium for their growth." 



Gosta Grotenfelt,^^ however, in his text-book on the " Principles of 

 Modern 13airy Practice," reasserts the statement of Von Freudenreich 

 that when the milk is drawn from the udder of a healthy cow, it is germ- 

 free or sterile. 



Rotch^^ concludes, from an examination of the bacteria found in 

 four cows' milk, that the bacteria do not necessarily come from external 

 sources, but that they may also come from some part of the milk-tract 

 between the udder and the end of the teat. The few colonies, however, 

 obtained in the plates from the latter half of the milkings, are considered 

 as possible contaminations between the " cow " and the " plates." 



Moore^^ states that in investigations made upon this subject, he 

 found that, in addition to the bacteria in the fore-milk, the last milk 

 from at least one-quarter of the udder in every case contained bacteria. 



Conn,^ reviewing this subject, says that the different results of 

 many of these early experiments are due to the small quantities of milk 

 taken, while in the latter experiments large quantities have been taken. 

 He adds, " Undoubtedly the milk-gland of the healthy cow produces 

 milk which is uncontaminated with bacteria, but the large calibre of the 

 milk ducts makes it possible for bacteria to grow in the duct to a con- 

 siderable extent, so that it becomes a matter of extreme difficulty to 

 obtain milk from the cow, even with the greatest precautions, which will 

 not be contaminated." 



Harrison,^ in 1897, in a report of investigations upon this subject 



