3 o MILK AND THE PUBLIC HEALTH CHAP. 



(c) Stale milk from dirty cans. Streptococci multiply 

 rapidly in milk, and they are often very abundant in the 

 traces of milk left in improperly cleaned milk cans. 



(cT) Cows suffering from mastitis. The relationship of 

 mastitis to streptococci is discussed in Chapter VI. It is 

 sufficient to remark here that in the secretions of cows suffer- 

 ing from mastitis due to streptococci these organisms are present 

 in extremely large numbers. In some instances plates brushed 

 with a single loopful of the fluid will show as many as a 

 thousand streptococcus colonies. 



The significance of streptococci in milk has been much 

 debated, and opinion on the subject has passed through two 

 distinct phases. The earlier investigators who found strepto- 

 cocci in milk for the most part inclined to the view that their 

 presence was, if not due to definite pathological lesions of the 

 cow, at least highly unsatisfactory, and fraught with potential 

 harm to the consumers of such streptococcus infected milk, 

 particularly if the consumers were young. 



Hoist, for example, isolated streptococci from milk supplied 

 by cows suffering from mastitis, and considered them to be the 

 cause of gastro-intestinal catarrh. Beck also believed that the 

 streptococci in milk were closely related to the streptococci 

 found by Escherich in cases of infantile diarrhoea, while Bergey 

 concluded that these organisms were probably not infrequently 

 the cause of serious gastro-intestinal disorders in infants. 



As already mentioned, later investigations have shown that 

 streptococci are extremely numerous in milk, are practically 

 present in all samples of mixed milk, and indeed are fre- 

 quently present in the milk of perfectly healthy cows. Also 

 Kruse, in 1903, and Rolling, in 1904, both working in Bonn, 

 advanced the view that the lactic acid bacilli of the B. acidi 

 lactici type were not bacilli, but streptococci. Heinemann, in 

 1905, independently came to the same conclusion. 



These facts and views have caused a modification of the 

 opinion that streptococci in milk are of necessity prejudicial, 

 and the view as to their significance now most commonly held 

 may be said to be one of tolerance qualified by suspicion. 

 Indeed, we can go further and postulate that if any significance 

 is to be attached to the presence of streptococci in milk it 

 must either be because 



