96 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
APHTHOUS FEVER OR FOOT AND MOUTH DISEASE 
In the milder forms of foot and mouth disease the 
milk secretion may not be affected, but in the more severe 
cases the milk flow is reduced one-half and the milk is con- 
siderably changed in composition and appearance. The 
alterations are similar to those observed in inflammation 
of the udder. The albumin, globulin and salts are in- 
creased in quantity, while the sugar, casein, and usually 
the fat are decreased, although sometimes the fat is in- 
creased. The milk becomes thin, and after it stands 
for a while a layer of slimy, dirty cream forms at the 
top of the fluid and considerable sediment is deposited 
at the bottom of the vessel. When examined microscopic- 
ally, the sediment is found to be rich in cells—epithelial 
cells, leucocytes, and red-blood cells. The milk coagu- 
lates when boiled, reacts positively to the alcohol test and 
contains a large amount of catalase. 
Nocard has shown that the milk of affected cows does 
not contain the virus of foot and mouth disease when it 
is drawn from the udder in a manner which pre- 
vents external contamination. But when vesicles or 
ulcers are present on the teats or udder it is not possible 
to draw milk in the ordinary way without it becoming 
contaminated with the virus. Merely a trace of the serum 
from the vesicles is sufficient to render 50 to 100 quarts 
of milk infectious. Practical experience indicates that 
the milk of affected cows is frequently infectious. Fur- 
thermore, the extraordinary facility with which the virus 
is disseminated makes it extremely probable that all of 
the milk of a herd in which the disease exists may be 
infected secondarily. 
The disease may be transmitted to man through milk, 
