252 BACTERIA IN MILK AND THEIR SOURCES 



FIG. 41. Plate exposed one minute in cowshed before 

 milking commenced. 



More attention should be given to the cleanliness of 



the milker, and his 

 freedom from ex- 

 posure to possible 

 disease which can 

 be transmitted 

 through milk, than 

 is generally the 

 case. 



Another source 

 of contamination ot 

 milk is the floating 

 matter of the air in 

 the cowshed. This 

 consists of dry par- 

 ticles of dung, dust 



from hay and other fodder, as well as many similar 



materials which are 



bearers of bacteria. 



Harrison found that 



the number of bac- 

 teria falling on a circu- 

 lar surface one foot in 



diameter (about equal 



to the opening of an 



ordinary milk pail) 



was from about 1 3,000 



to 40,000 per minute 



in a cowshed where 



the cows had just been 



bedded. About an 



hour later much of the 



dust had settled, and the number deposited on a similar 





FIG. 42. Plate exposed one minute while milking 

 was being done. 



