THE NATURE OF THE AMERICAN SWINE PLAGUE. 
299 
or upon an infected locality, or to come in contact with something 
derived from such a locality, such as the earth itself, or grains, 
hay, grasses or roots grown upon such earth. Such diseases are 
strictly local in their primary origin. 
There is a phenomenon, however, in connection witli many of 
these primary local infectious diseases which has led, and, unfor¬ 
tunately, still leads to an immense amount of unnecessary confu¬ 
sion and misunderstanding, which it is very essential should be 
cleared up. 
Attention has been previously called to the fact that suscep¬ 
tible animal organism, in case of primary infection, must be in or 
upon such infected localities. Such localities form the (so called) 
fixed or natural centers of infection. These fixed or natural cen¬ 
ters of infection are to be looked upon in a far different light than 
animals infected with a contagious disease, though they also form 
the only natural centers of primary infection. The primary cen¬ 
ter of infection in contagious diseases is movable. The danger¬ 
ous principle bound upon it is not fixed in any given locality. 
The infected animal in contagious diseases is the primary, while 
in infectious diseases it is a secondary center of infection. Here, 
again, we have an animal organism acting as a movable center of 
infection, but not contagion —that fact must not be lost sight of. 
Such animals can infect other localities, but not other animals di¬ 
rectly, in the sense that contagious diseases pass from animal to 
animal. 
The living animal then becomes a traveling medium of infec¬ 
tion, and although of itself not directly dangerous to other ani¬ 
mals, yet in many diseases such an infected individual is far more 
dangerous than one affected with many contagious diseases, though 
it takes longer for the danger to become apparent. 
Such an animal can infect the localities in which it comes. 
While the animal afflicted with a contagious disease can also leave 
effluvia that may be dangerous for a time, it soon dies out, but 
this other animal leaves seed that, the conditions being favorable, 
develops and multiplies, giving occasion to the infection of other 
animals, and they to other localities, and so the destroyer gradu¬ 
ally extends over a country, seldom marking its course by a gen- 
