28 MILK AND THE PUBLIC HEALTH CHAP. 



but only the harmful or potentially harmful, and those whose 

 presence may be taken as an index of general or special 

 pollution. 



The butter-maker and the pure scientist are in a different 

 position, and have much to gain from a full knowledge of all 

 the kinds of bacteria met with in milk. 



It will be sufficient for public health purposes to describe 

 the chief groups of bacteria met with in milk, and to discuss 

 the significance of their presence and the sources of entry. 



The following groups are considered : 



Group 1. Streptococci and staphylococci. 



2. Bacillus coli and allied organisms. 



3. The lactic acid bacilli. 



4. Spore-bearing bacteria in milk. 



5. Acid fast bacilli. 



The pathogenic bacilli, such as B. tuberculosis, are described 

 in subsequent chapters. 



It may also be mentioned that a number of interesting 

 chromogenic bacilli are known to occur in milk. Of these 

 may be mentioned B. prodigiqsm, associated with red milk ; 

 B. cyanogenus, the cause of blue milk ; B. synxanthus, the cause 

 of yellow milk. 



Special organisms concerned with the production of bitter 

 milk, soapy milk, etc., have been isolated. 



Although these bacilli are of considerable interest, they are 

 of little or no importance in relation to public health, and are 

 therefore not discussed in detail. 



GROUP 1. STREPTOCOCCI AND STAPHYLOCOCCI IN MILK 



Streptococci. Streptococci are undoubtedly very prevalent 

 in ordinary samples of market milk. They are not only very 

 numerous in milk as vended, but are often abundant in 

 samples of mixed milk collected immediately after milking at 

 the farmland examined before any multiplication can have 

 taken place. The writer has found streptococci present in 

 every sample of mixed milk (although many were collected 

 at the farm) which he has examined, when 1 c.c. was sampled, 

 and in over 80 per cent when O'l c.c. was examined. Orr 



