in THE BACTERIA FOUND IN MILK 31 



(a) Their presence is an indication, and their numerical 



presence an estimate, of undesirable pollution — that 

 is, they act as indicators of pollution, and quite 

 apart from any potential harmfulness of their 

 own ; or 



(b) They are so numerous that their presence can only 



be explained as derived from a pathological lesion 

 of the cow ; or 



(c) Certain definite varieties are present which are known 



to be associated with pathological lesions, and to 

 play a disease-producing role in man. 



The possible value of streptococci for these purposes may 

 be briefly considered. 



As indicators of manurial pollution they have this in 

 their favour, that, as mentioned above, they are abundant in 

 the materials whose presence we wish to quantitatively measure. 

 The fact that they are found in milk drawn direct from the 

 teats is fatal to their use for this purpose, since to judge the 

 cleanliness of the methods used in milk collection, etc., by a 

 test which is in part independent of such conditions, cannot be 

 considered a satisfactory procedure. 



Whether the presence of enormous numbers of streptococci 

 in fresh milk can be utilised as a reliable indication that the 

 milk is in part derived from animals suffering from local patho- 

 logical lesions of the udder or teats is at present undecided. 

 Certain is it that in cow mastitis, some cases of teat ulceration, 

 etc., the lesions show streptococci present in enormous numbers. 

 In one instance the writer found that when the cows of a 

 cow-keeper whose fresh milk contained enormous numbers of 

 streptococci were examined severe teat ulceration, associated 

 with abundant streptococci, was found upon several of the cows. 



While streptococci as a class cannot be at once condemned, 

 it is of the utmost importance, in view of the fact that 

 streptococci are amongst the most harmful of bacteria known 

 to man, to study the different varieties present in milk, and 

 to endeavour to separate the pathological and harmful types 

 from the saprophytic and harmless. 



Unfortunately the differentiation of streptococci is by no 

 means satisfactory, nor is the basis of classification uniform 

 for different workers. Some investigators rely solely upon 



