162 



CITY MILK SUPPLY 



the air of stables is much less important than has been thought and that 

 a reasonable amount of care in avoiding extremely dusty operations 

 during milking will suffice to protect the milk adequately. 



Thus the quantitative microbial pollution of milk by stable air is 

 fairly well understood but there is little known about the relative im- 

 portance of the germs of different groups in the air-borne contamina- 

 tion that does occur. Bacteria yeasts and moulds are all found in stable 

 air. Among the bacteria certain micrococci are common and so are 



Courtesy of J. O. Jordan. 



FIG. 30. New England barn of the type in which the air is seriously contaminated in 



feeding the hay. 



organisms of the B. subtilis group. Bacteria of the B. coli-Bact. lactis 

 aerogenes group may be swept into the air with particles of dung and 

 from other sources. Disease germs are uncommon in the air but to 

 some extent Bad. tuberculosis and other pathogens may circulate in the 

 air in infected stable dust. In a goat stable, if there are animals which 

 have been imported from Mediterranean countries, the dust is likely 

 to be infected with M. melitensis. Mould spores are common in stable 

 air but yeast is less so than are either bacteria or moulds. 



Contamination from Feeds. Feeds of various sorts are often rich in 

 bacteria that become attached to the leaves or kernels of grain of the 



