METHODS OF EXAMINING MILK 283 
and if streptococci are present. In fresh cows, the sedi- 
ment is usually of a grayish-white or white color and or- 
dinarily does not exceed 0.08 per cent; sometimes the 
sediment is red, which is an indication of the presence of 
red blood cells. 
Tn all of these tests the kind of leucocytes should re- 
ceive attention as well as the number. 
A preponderance of polymorphonu- 
clear leucocytes is very significant, 
since in mastitis three-fourths and 
more of the cells are of this type. The 
clumping or grouping of the cells is 
also characteristic of milk containing 
mastitis secretion. There is an in- 
creased number of epithelial cells in 
the milk of cows affected with mas- 
titis; in catarrh of the milk cistern, 
nests of elongated epithelial cells may 
be observed in the sediment. 
When an excessive number of leu- 
cocytes is found in market milk, with 
a preponderance of polymorphonu- 
clear cells showing the characteristic <u 
clumping or grouping, an examination x6, 39,—sediment tube 
of the herd from which the milk came tes, showing) eraduations 
will usually disclose the presence of % the bottom. 
mastitis or other suppurative condition. In such cases, 
however, it must be remembered that leucocytes are in- 
2sreased in number in the milk at the beginning and near 
the end of lactation and following incomplete or delayed 
milking. Heating milk to 60° C. (140° F.) or above 
also increases the number of leucocytes in the sediment. 
When the number of leucocytes in market milk falls 
