6 THE CONTAMINATION OF MILK. 



floor, if the stable be free from draughts. Brushing just before 

 milking will usually double the number of bacteria that would 

 otherwise have gained entrance during milking (60). In the 

 best dairies the switch of the tail is washed before the milking. 

 Precautions are taken to prevent switching, by the use of a tail 

 holder (Ref. 8, Chap. IX). 



Exterior of udder. The udder and teats are especially ex- 

 posed to filth, either from the barn-yard or the stable floor when 

 the cow is lying down. The movements of the udder, during 

 milking, tend to constantly dislodge dust and hair which fall 

 into the milk pail. Dairy practice should include the washing 

 of the udder and teats before milking, when filth is present, 

 and the dampening of the hair whether dirt is present or not. 

 If the udder is left dripping wet, the dirty water will become 

 a source of contamination of the milk. The dampening causes 

 the dust to adhere to the hair and largely eliminates an im- 

 portant contaminating influence. If the hair of the udder is 

 kept clipped short, the cleaning is greatly 'facilitated. The 

 value of dampening the udder may be demonstrated by a simple 

 bacteriological experiment. Sterile Petri dishes, containing a 

 suitable solid culture medium, may be exposed under the 

 udder for half a minute during milking before and after damp- 

 ening. After the lapse of time sufficient to permit bacterial 

 growth, the number of colonies of bacteria showing on the 

 two plates will exhibit a wide difference in the number present 

 in favor of dampening (51). The number of bacteria shaken 

 from apparently clean udders may be reduced by two-thirds, 

 by merely dampening. The possibilities of contamination, 

 from really dirty udders, are enormous. By dampening the 

 udder and flanks the contamination may be reduced to about 

 ten percent, of that which would otherwise have occurred (60). 



In the certified dairies maintaining the greatest aseptic pre- 

 cautions, the methods of cleansing the udder are very carefully 

 considered. Practice varies, but the following method will 

 suffice to illustrate the point : Wipe udder and adjoining parts 

 with burlap to remove particles of bedding, wash with luke- 

 warm water applied with a cloth, spray with lukewarm water, 

 wipe W 7 ith a freshly laundered bath towel. This is so folded 



