98 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
udder they are round; on the teats oblong, with the great- 
est diameter parallel with the length of the teat. In a 
day or two they change into vesicles of a bluish-white 
or yellowish-white color. The vesicles ripen into pustules 
in eight or ten days and a depression or umbilication 
appears in the top, after which they rupture and leave 
an ulcer, or dry and heal under a scab. They may be 
ruptured during milking before they are ripe. 
The milk may become thin, bluish, and of lighter 
specific gravity than normal; it may be nauseating and 
may coagulate very readily. The acidity may be below 
normal. These changes, however, do not always occur. 
When the disease is complicated with parenchymatous 
mastitis, as sometimes happens, then the milk undergoes 
the pronounced changes which occur in the latter con- 
dition (see page 109). 
Cowpox is transmitted from cow to cow by the milker 
and by infected bedding, fodder, and stalls. The disease 
is also transmissible from the cow to man through milk. 
There is no proof that the virus is excreted through the 
udder, but as the pox are located on the teats and the 
adjacent parts of the udder it is practically impossible 
to draw the milk without the virus contained in the ves- 
icles and pustules getting into it. Stern saw cowpox 
transmitted to a large number of children by milk from 
a dairy in which the disease was enzodtic. The children 
were affected with an eruption on the face which healed 
under a scab. Not many such observations have been 
recorded, however. The reason for this is that the general 
custom of vaccinating against smallpox has rendered 
most persons immune to the disease. The transmission 
of the disease to the milkers by direct infection of wounds 
on the hands or fingers has been more frequently ob- 
