INFLUENCE OF DISEASE UPON MILK 113 
BLOOD IN MILK 
A mixture of blood with the milk may occur as a 
result of traumatisms of the udder, such as kicking, hook- 
ing or treading, which cause hemorrhages or blood infil- 
trations into the udder tissue. The pulling or dragging 
to which a greatly distended udder is subjected when the 
cow walks may cause a tearing of the udder tissue which 
will permit the mixing of blood with the milk. When 
large blood vessels have been injured the milk is colored 
diffusely red. But when small vessels are torn or rup- 
tured, which is more often the case, only small streaks of 
blood are observed which disappear when the milk is 
shaken and do not discolor it. When such milk is centri- 
fugalized, the sediment shows a red color which, on micro- 
scopic examination, is found to be due to the presence 
of red-blood cells. Blood is observed in the colostrum 
or milk during the first week following parturition in 
those cases in which the udder is intensely hyperemic, 
resulting in a diapedesis of red-blood cells. 
(@DEMA OF THE UDDER 
Sometimes, especially in heifers with the first calf, 
the udder becomes very much swollen and cedematous 
shortly before parturition. The swelling is not hot, nor 
is it painful unless the skin is intensely stretched; it 
disappears a few days after parturition. Usually, no 
essential changes are observed in the milk. It is probable 
that some of the serous transudate is mixed with the 
milk, but nothing definite is known on this point. Some- 
‘times the milk contains blood. Generally, the oedema 
has disappeared by the time the colostral stage is passed. 
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