HUMAN AND ANIMAL VARIOLAS. 
59 
tive tissue. In the equine species, and particularly young 
animals, there sometimes occur magnificent pustular erup¬ 
tions, which, in their seat and general characteristics, differ in 
nothing from natural horse-pox. These vaccinal eruptions have 
never been observed in the experiments on the bovine species, 
though they were numerous, and made under those conditions 
which are reputed to be the most favorable to the development 
of the so-called “ spontaneous cow-pox.” These eruptions have 
never been witnessed in experiments on man, though it must be 
confessed that the number of these was small. 
But the negative results in the human and bovine species do 
not authorize the conclusion that these are refractory to the mani¬ 
festation of the vaccinal eruption in the before mentioned condi¬ 
tions. But they demonstrate this important fact, that so far as 
aptitude for the development of this exanthem is concerned, the 
organism of the horse possesses an incontestible superiority. 
“4. This superiority is manifest equally,whether the vaccine virus 
is introduced directly into the lymphatic or blood-vessels, or enters 
by the natural channels of absorption. The intravenous injection 
of vaccine matter—the most certain and easiost of these experi¬ 
ments—does not appear capable of producing vaccinal immunity 
in bovine animals. But in the horse not only does it ensure this 
immunity, but it often produces the vaccinal exanthemata which 
are an exact fac simile of those of the natural disease. 
“ 5. The results of this experimental study show as well, if 
not better, than clinical observation, that the horse has a special 
aptitude for the natural and spontaneous development of vaccinia, 
either under the influence of occult contagia , or by the proble¬ 
matical intervention of any other equivalent cause which has yet 
to be ascertained. The bovine species is far from manifesting 
such an aptitude for the evolution of natural vaccinia. It might 
even be asserted that, in this respect, the ox is not superior to the 
human species—at least it is certain that the inferiority of the 
latter has not been demonstrated. 
“ From this study it is evident—and the evidence is further 
fully confirmed by clinical facts—that the organism of the horse 
is the real source (vraie patrie ) of natural vaccinia, conformably 
to the views of Jenner.” 
