6O PRACTICAL DAIRY BACTERIOLOGY 



care. By extreme precautions in special tests small quantities 

 of -sterile milk have been thus obtained; but these precautions 

 are not practical in ordinary milking, so that the dairyman 

 must recognize that he cannot by any means of milking obtain 

 sterile milk. 



Bacteria in the Milk Ducts. The types of bacteria which 

 come from the milk ducts are varied. They are mostly cocci 

 and usually are not very numerous. Some of them liquefy 

 gelatin and peptonize casein, while others do not; some 

 produce small quantities of lactic acid while growing in milk, 

 but others have no appreciable action on milk. These udder 

 bacteria do not, as a rule, contain any representatives of the 

 common lactic acid types, since neither Bact. aerogenes nor 

 Bact. lactis acidi are common inhabitants of the glands or milk 

 ducts. A very few cases have been found in which the latter 

 organism is present in considerable abundance in the milk ducts. 

 But all experimenters agree that this is an unusual occurrence, 

 and that whereas it does occur in some cases, the general rule 

 is that milk drawn directly from the milk ducts does not con- 

 tain the lactic acid organisms, which in older milk are by far 

 most common. In recent years the presence of Streptococci in 

 milk has been sometimes regarded as rendering the milk sus- 

 picious for reasons already noted. It is very important to notice, 

 therefore, that the freshest milk from the best of cows is prac- 

 tically sure to contain Streptococci coming directly from the 

 udder. The cocci thus found appear to be similar to, if not 

 identical with, some of the widely distributed forms that are 

 commonly associated with inflammatory processes. (Strepto- 

 coccus pyo genes, etc., Staph. aureus and Staph. albus, etc.) 

 Whether they are identical with them it is difficult to say, but 

 at all events their presence in milk cannot be a ground for 

 condemning milk, unless it be to condemn all milk as an 

 article of food; for otherwise nearly all fresh milk would be 

 condemned. As a rule, the Streptococci in milk do not form 



