96 
F. 8. BILLINGS. 
Not only the individuals of the single species, but the latter 
also deport themselves in a very variable manner towards the 
contagia of these infectious diseases. While the animals remain 
to all intents immune from the epidemic diseases of man, even 
cholera and typhus, all assertions to the contrary, man is suscep¬ 
tible to the contagium of quite a number of animal pests ; as ex¬ 
amples, malleus, anthrax, rabies and aphtlue epizooticse. We 
find very great differences with regard to the disposition (suscep¬ 
tibility) of the different species for the contagii of the zoonoses: 
while a succession of animal-species, inclusive of man possess an 
equal susceptibility for the contagium of rabies ; and swine and ru¬ 
minants possess a great susceptibility for that of aphthae epizooticse ; 
man possesses but little, and solipeds and carnivora still less. Iler- 
bivora are very susceptible to the action of the contagium of an¬ 
thrax, while the omnivora, inclusive of man, are much less, and car¬ 
nivora have but a very slight disposition for the same. Malleus is 
in general limited to solipeds, the remaining animal creation, in¬ 
clusive of man, having but a relatively insignificant susceptibility 
to the contagium of the same ; cattle none. While the contagium 
of rinderpest sometimes affects sheep and goats, all other animals 
remain immune from the action of the same pleuro-pneumonia 
bovine contagiosa is limited exclusively to cattle as syphilis to man. 
In this direction the variolse offer the most attraction, because 
they not only attack man, but nearly all the domestic animals, 
and because of the genuine culture historical importance, which 
the artificial transmission of an animal variola to man has won in 
a prophylactic point of view; a service which has rendered the 
name Jenner immortal, in that the sting is thus, in part at least, 
removed from perhaps the most formidable scorpion which has 
tortured the human race. 
It becomes us now to seek to acquire a general idea of the 
present stand of the variolic theory, from the standpoint of 
general pathology, and thereby to critically consider their re¬ 
ciprocal relation and especially their reciprocal transmission to 
other species and (vice-versa retrovacination). This territory is how¬ 
ever so extensive, and many questions so imperfectly considered, 
that the result of our study must necessarily be more or less im- 
