Contamination of Milk. 21 



Sources Of infection. The bacterial life that finds its 

 way into milk while it is yet on the farm may be traced to 

 several sources, which may be grouped under the following 

 heads : unclean dairy utensils, fore milk, coat of animal, 

 and general atmospheric surroundings. The relative im- 

 portance of these various factors fluctuates in each individ- 

 ual instance. 



Dairy utensils. Of first importance are the vessels that 

 are used during milking, and also all storage cans and 

 other dairy utensils that come in contact with the milk 

 after it is drawn. By unclean utensils, actually visible 

 dirt need not always be considered, although its presence 

 in cracks and corners of pails and cans is often the 

 case. Unless cleansed with special care, these cracks and 

 joints are apt to be filled with foul and decomposing ma- 

 terial that suffices to abundantly seed the milk. Soxhlet 1 

 found that the addition of 0.1 per cent of sour milk to 

 fresh milk decreased the keeping quality of the latter from 

 15 to 30 per cent ; the addition of 1.5 per cent diminished it 

 80 per cent. Where cans are not well cleansed the above 

 amount could easily be added to the milk from the ma- 

 terial that adhered to the walls of the can. 



Through negligence, vessels are often used that are unfit 

 for handling milk. A rusty milk-can often spoils more 

 . milk than sufficient to purchase a new ves- 



\ / sel. Wooden pails are no longer tolerated in 



\ J^ a well-regulated dairy. Where possible, ves- 

 sels should be made of pressed tin. If join's 

 are necessary, they should be well flushed with 

 FIG. 6. solder so that they may be easily and thor- 

 oughly cleaned as shown in Fig. 6. In much of the 



1 Soxhlet, Ber. d. Wandervers. bayer. Landwirthe, Oct., 1894. 



