Contamination of Milk. 37 



with the same, if it is done immediately after the milk is 

 drawn. The only objection to this process is that the 

 cream does not rise so thoroughly as where it is not cen- 

 trifuged, but the other advantages where an especially 

 clean milk is wanted more than compensate for this 

 defect. 



41. Influence of air. It is impossible to separate 

 the influence of the air entirely from that of the animal, 

 as the dust particles from the coat of the animal must 

 of necessity pass through the air. 



FIG. 8. Effect of contaminated air. Each spot on this surface represents 

 a developing colony that has grown from a germ that was deposited on surface 

 of a sterile gelatin plate (3 inches in diam.) in 30 seconds. This exposure was 

 made at time the cows were fed. 



Germ life cannot develop in the air, but in a dried con- 

 dition, organisms retain their vitality for long periods of 

 time. The use of dry fodder, the bedding of animals 

 with straw adds greatly to the amount of dust particles, 

 and consequently the germ life floating in the air, as 

 seen in fig. 8. Taints in milk have frequently been 

 traced to infection arising from this source. 



