xi EXAMINATION OF MILK 199 



inspection frequently cannot furnish, and the procedure reaches its 

 highest utility when combined with a bacteriological examination of 

 the milk. 



It is certainly unjustifiable to lay down rigid standards of 

 the number of leucocytes to permit in milk, as has been done 

 by some American bacteriologists. When present in numbers 

 more than 800 to 1000 per cubic ni.m. they indicate the need 

 for careful enquiry as to the local condition of the cow's udder 

 or teats. 



Dealing with this estimation in mixed milk samples, it is 

 obvious that it can in no way assist in the determination of 

 the bacterial pollution of milk, but it might be considered 

 that the cellular count is of value as a means of detecting the 

 presence of purulent inflammation of the udder of one or more 

 of the cows composing the herd yielding the mixed milk. 

 The writer has never held this view, since on purely mathe- 

 matical grounds it seems unlikely that leucocyte enumerations 

 of mixed milk samples would be of use to detect purulent 

 inflammation in one or more of the cows. This may be shown 

 most clearly by a concrete instance. 



In a herd of 20 cows it is assumed that one animal is affected 

 with mastitis in two quarters, and that the secretion from these 

 quarters is added to the milk with the rest. A reasonable sup- 

 position is that as many as 100,000 leucocytes per cubic m.m. are 

 obtained from each affected quarter, and that the yield from each 

 of these quarters is as much as ^V of the normal amount yielded 

 per quarter. It is hardly likely to be more than this, and if more 

 were obtained it would certainly contain less than 100,000 leucocytes 

 per cubic m.m., so that the total number of cellular elements added 

 would be but little altered. The average number of leucocytes per 

 cow may be taken as about 680 (average of a large number of 

 examinations by the writer). The increased number of leucocytes 

 in the added milk due to the addition of the fluid from the diseased 

 quarters can now be readily calculated. 



Let x = the average amount of milk yielded per quarter. Then 

 the total number of leucocytes from the 19 cows with healthy 

 quarters = (19 x 4) .7; x 680 = 51,680ff. 



The total number of leucocytes from the cow with two diseased 



quarters = (2 x a x 680) + ( 2 X x x l^ * ^ = 2 l } 360z ; .-. the total 



number of leucocytes in the whole of the mixed milk 51,680$ 

 + 21,360= 73,040a;. 



