HUMAN AND ANIMAL VARIOLAS. 
191 
tion. It is the same with the pig. In the sheep a small papule 
generally forms at the seat of inoculation, with rarely a little ves¬ 
icle that rapidly becomes encrusted. Re-vaccination from this to 
calves gives negative results. 
Not only in their special characters do the variolae of man 
and animals differ, but also in their apparent mode of extension. 
Human variola and sheep-pox differ widely from each other in 
some respects, particularly in their not acting antagonistically, 
and in the appearance of the eruption, but they are identical so 
far as their diffusion is concerned. They are both infectious and 
contagious, and can be transmitted by fomites, as well as by- 
actual contact; while their virus possesses a vital resistance some¬ 
what remarkable. • Cow-pox, horse-pox, and the variolae of other 
animals would appear to depend for their dissemination upon 
their contagious properties only, and their virus readily becomes 
deteriorated. 
There are other peculiarities in the variolae of man and animals 
which' still further differentiate them, but these I shall not allude 
to here; so pass on to the consideration of the far more pressing 
question as to .the identity of small-pox and cow-pox. and an ex¬ 
amination of the arguments brought forward in support of this 
identity. But before doing so, I may as well confess that I do 
not for a moment hold with the abiogenetic or “spontaneous” 
origin of variola either in man or beast, and am prepared to 
maintain that whenever and wherever, and in whatever species 
the disease manifests itself, it is always due to its own special con- 
tagium, no matter how this may be conveyed. 
It has been stated that cow-pox is now a very rare disease, and 
that the probable cause for its being more frequent in the days of 
Jenner was the much greater prevalence of small-pox; thus lead¬ 
ing to the inference that the one disease was dependent on the 
presence of the other. But this statement will not bear close ex¬ 
amination. We have no definite evidence to prove that cow-pox 
was a common disease before vaccination became general, nor 
yet that it is a very rare malady now; still less that its frequency 
had any relation to the occurrence of small-pox. We have only 
the testimony of Jenner, and two or three other observers of the 
\ 
