CONTAMINATION OF MILK 61 



farm separator and the milking machine, where this is in use. 

 On many farms the separators are not taken apart for wash- 

 ing after each period of use, but the apparatus is rinsed out 

 with water, either hot or cold, and left in an assembled con- 

 dition. Sometimes the machine is taken apart and thor- 

 oughly cleaned only at considerable intervals, such as once a 

 week, reliance for cleanliness being placed on the use of a solu- 

 tion of washing powder and subsequent rinsing with water. 



The long rubber tubes which are necessary with the milk- 

 ing machine cannot be cleaned perfectly, and must be kept 

 in an antiseptic liquid in order to prevent bacterial growth. 

 For this purpose limewater or a weak solution of formalin 

 is preferably used, although brine solutions have sometimes 

 been recommended. 



The number of bacteria adhering to any utensil, will de- 

 pend upon the condition of the surface. If it is smooth, as 

 in a new, well-tinned pail, the number will be much less 

 than if the surface is roughened by rust. The difficulty in 

 rinsing the milk from even a perfectly smooth surface can 

 be illustrated by filling a pipette with whole milk and then 

 trying to remove all visible traces of the milk by passing a 

 stream of water through it. 



If the milk is allowed to dry on a utensil, it is impossible 

 to remove it by ordinary means, since the casein when dried 

 forms a glue-like substance, which softenfe in water very 

 slowly and can be removed only by scouring. 



Cloth strainers are likely to add more bacteria to the milk 

 than they remove, unless they are so treated as to prevent all 

 growth in the cloth. A strainer well rinsed in cold water, 

 then in boiling water, wrung dry, and hung in the sun, or 

 where it will dry rapidly, will contain small numbers of bac- 

 teria. A strainer simply rinsed in cold or lukewarm water 



