THE NATURE OF THE AMERICAN SWINE PLAGUE. 
409 
This transmissibility, I wish again to emphasize, has nothing 
to do with the natural peculiarities of such diseases in most cases. 
It simply shows that they are capable of inoculative transmission, 
either by accident or experiment. 
Although we know absolutely nothing as to the physiological 
conditions upon which this racial, or natural, predisposition de¬ 
pends, still empiricism has shown its existence to be a most ex¬ 
pensive biological fact. To its existence are directed all our 
endeavors at prevention by means of artificial inoculation with 
a modified virus—a subject I will not touch upon further at 
present. 
It is generally a much easier question to arrive at the fact 
that a given disease is contagious (if we only know what we mean 
by that word), and to combat the extension of such a disease, than 
it is to understand and successfully prevent such an infectious dis- 
ease as the swine-plague or the Asiatic cholera. 
In the first, we render all contact impossible between healthy 
and sick or exposed individuals or their surroundings. In the 
case of animals, we kill the diseased ones, and if necessary the 
exposed; we air the stables and subject them to a suitable cleans¬ 
ing and disinfecting, and our work is done. 
In other words: In contagious disease we seek to do away 
with the living, movable, primary centers of contagion, or to so 
restrict the movements of such objects, that no susceptible organ¬ 
isms can come in contact with them. In infectious diseases we 
have to do with numerous fixed centers of danger (infection) as 
well as numerous living, moving, transient centers, capable of 
causing innumerable newly infested fixed centers of danger. 
Aside from these, we have the infected material itself, which must 
be kept local, and also so change these local conditions as to ren¬ 
der them unsuitable to serve as a medium of support and devel¬ 
opment to the inficiens proper. 
It is easy to be seen that between two devastating diseases— 
say, pleuro-pneumonia and swine-plague—-it is a much easier mat¬ 
ter to stamp out and prevent the contagious than it is the infec¬ 
tious disease. 
It will also be found that where vaccination or preventive in- 
