476 COW POX 
Experiments have shown that horses and cattle may be immunized 
with variola against cow pox and man with vaccinia against variola 
but a similar reciprocal action between the diseases of man and sheep 
does not seem to exist. % 
COW POX 
Synonym: Vaccina. 
Characterization. Cow pox is an acute infectious disease affecting 
chiefly milch cows, characterized by slight temperature disturbances 
and the appearance of an eruption on the skin of the mammary gland 
and teats which passes through the stages of papule, vesicle and pus- 
tule scab. It is transmitted to the horse and man by actual contact 
or by inoculation. When inoculated into man it produces a more or 
less permanent protection against small pox. This fact led Jenner in 
1796 to introduce vaccination of the human species with the virus of 
cow pox to protect them against small pox. 
Etiology. The virus of cow pox has been passed through the porce- 
lain filters by Negri, Remlinger and others. Proscher reports that he 
has cultivated the virus on artificial media, prepared especially for 
this purpose. His results do not seem to have been confirmed. It 
resists drying for several weeks but is destroyed at a temperature of 
57.5° C. in five minutes. It is not affected by freezing. When 
mixed with glycerin it will remain virulent from 8 to 10 months. 
Natural infection generally takes place during milking when the virus 
is usually transmitted from one cow to another on the hands of the 
milkers. 
The period of incubation is from 4 to 7 days when the infection 
is contracted in the usual manner. After direct inoculation it is from 
2 to 4 days. 
Symptoms. The first evidence of cow pox is a slight rise in tem- 
perature, impaired appetite, irregular rumination and weakness. In 
many cases these symptoms are exceedingly slight. The udder 
becomes somewhat sensitive, the milk is said to be thinner and to 
have a lower specific gravity and to coagulate more quickly. The 
eruption is described under the morbid lesions. 
The duration varies up to 30 or 40 days depending upon the number 
of successions of vesicles. 
Morbid anatomy. On the slightly warmer and swollen teats as 
well as on the adjoining parts of the udder, nodules ranging from 1 to 5 
