190 
GEORGE FLEMING. 
see immediately, though the virus of human small-pox, when 
deposited in the skin of the cow, does give rise to a local 
papulation—often very trifling, exceptionally very marked—yet 
this is not the regular eruption of cow-pox, either in its appear¬ 
ance or course, and it does not prevent the cow being successfully 
vaccinated at the same time, though it appears to destroy the apti¬ 
tude to receive vaccinia; while in two or three transmissions througli 
the bovine species it becomes altogether impotent. The same re¬ 
sults are observed in the horse, which, however, appears to receive 
the virus of human small-pox more readily, and to exhibit more 
marked local phenomena than the ox; while this inoculation also 
protects it partially, if not entirely, from the action of vaccine 
virus, which it otherwise so readily receives. As in the ox like¬ 
wise, the small-pox virus soon loses its potency in being carried 
from one animal to another—it cannot be cultivated in them ; 
and experiment has demonstrated, that no more in the organism 
of the horse than in that of the ox can human variola be transmu¬ 
ted, but that after passing through the bodies of solipeds, and again 
transferred to man, it has lost none of its characteristic features. 
Cow-pox can be very readily transferred to man, the ox, horse, 
and goat, the first three showing an equal aptitude for its recep¬ 
tion ; in them also the transmission of the disease is indefinite— 
i. e., the virus may be cultivated, without impairment, for a limit¬ 
less number of generations, and it confers immunity against the 
variola of man and the horse, while the ox itself is protected. 
But while vaccination only produces in man and the ox a local 
and limited eruption, in the horse it often produces a startling 
pustular exanthem, which, in character and seat, differs in nothing 
from natural horse-pox. Another peculiarity in the action of the 
vaccine virus in the horse is its tendency to produce this vaccinal 
eruption, and at the same time to confer immunity, when intro¬ 
duced directly into the lymphatics or blood-vessels; while in the 
ox it does neither under this condition—all circumstances which 
would lend support to the opinion of Jenner, that the horse is 
reallv the true source of natural vaccinia. 
•j 
Vaccination in the dog usually only produces small red nodules 
at the punctures, but nothing at all resembling the vaccinal erup- 
