EXPERIMENT STATION BULLETINS. 195 



On the other hand, where the precaution was observed to remove some 

 milk before the insertion of the milk-tube, a larger portion of the samples 

 was sterile. In working with contagious mammitis, the author has 

 obtained pure cultures of Noeard's streptococcus by following the 

 method above. This method is described in Bulletin 140, page 101. 



CONTAMINATION OF MILK AFTER LEAVING THE UDDER. 



It is not my intention to give practical methods to be observed in the 

 perfection of cleanliness about the cow, barn and dairy. My province is 

 confined to the habits of bacteria and their relation to milk. To avoid 

 their access to milk, I shall simply offer general suggestions. Some of 

 these may seem anticipatory and impracticable, still we live in an age 

 of progress and changes, and hope to see feasible methods realized some 

 day. It must not be expected that the dairyman and bacteriologist 

 will accord in these matters; both will, however, work in unison to a 

 satisfactory solution of the problems in hand. 



As soon as the milk has escaped the duct of the teat, the chances of 

 contamination have multiplied greatly. The avenues of access have 

 increased and may be considered under: exposure to the air of barn and 

 dairy; exposure to the filth from the cow; exposure to the particles of 

 dirt from the milker; exposure to the milking and dairy utensils. 



Exposure to Air of Barn and Dairy. — The number of bacteria varies 

 with the locality and circumstances. The air over a meadow is com- 

 paratively free from bacteria; in the city air the number has multiplied 

 a thousandfold, and if we pass on to the air of a cow stable, 

 the number has increased several thousand fold over that of the city. 

 Unless each individual is willing to make an experiment for himself, 

 he will appreciate in a small degree the contaminating power of 

 the cow stable air. This knowledge may be gained in a crude way by 

 exposing a smooth surface, as glass, to the air of a stable for a few 

 minutes, and while the exposure is being made watch the small, almost 

 imperceptible particles of dust falling upon it. Each particle repre- 

 sents by no means a single microbe, but scores of them which adhere to 

 the surface. As each particle becomes dissolved in milk those germs 

 which are hidden within its interior are liberated for activity. 



Currents of air serve to facilitate the travel of these micro-organisms. 

 Bits of decomposing matter, pieces of straw from the manure heap, 

 and the pulverized dirt and dung of the stable and barnyard are picked 

 up and borne along, and part of them will find their way into the milk. 



Any disturbance of dust must be avoided. The handling of hay at the 

 time of milking or before only adds many fold to the germ content of 

 the air. The stirring of the bedding is obnoxious. The hay and straw 

 are loaded down with bacteria awaiting only a suitable food in which 

 to grow. 



In a well kept dairy the air bacteria are not numerous. The dairy I 

 now have in mind has a cement floor and a good drain; with these two 

 agencies it is possible to keep down the dust. Where there is a board 

 floor, unless it is kept exceptionally clean, there is always a stream of 

 dust, visible or invisible, rising when passing over it. In such instances 



