FRANK S. BILLINGS. 
298 
Exogeneous—malarial—infectious, or absolutely local infec¬ 
tious diseases, in which the animal organism plays no part in their 
extension. 
The peculiar or idio-pathogenetic characteristics of the infi- 
ciens, in each case, decides the special nature of the disease. 
Swine.plague is a disease having a purely infectious charac¬ 
ter (anthrax, Texas fever, Asiatic cholera, are well known exam¬ 
ples of the same class of diseases). It is a disease in which the 
inficiens finds its primary, original development outside the por¬ 
cine organism. Genetically speaking, the inficiens is extra, and 
never of primary intra-organismal origin. 
The inficiens finds its suitable media for natural development 
in the earth and refuse earthy materials, and requires certain con¬ 
ditions of moisture, heat and chemical constituents to its support 
and progressive development. 
These facts established, we have discovered the nature of a 
given disease, and the key to practical methods of prevention. 
While we may never have seen the inficiens, we have discovered 
where it lives and thrives, under what conditions it does this, and 
by keeping susceptible animals away from such places for a given 
period, and by altering the conditions so as to render them un¬ 
favorable to the existence of the inficiens, by confining the dis¬ 
eased animals, and .other precautions to be mentioned hereafter, 
we have the principal effective means of preventing infectious dis¬ 
eases at our command. 
This has been possible with anthrax. Where intelligently ap¬ 
plied, localities that were absolutely unsafe for cattle, horses or 
sheep to graze upon, have been rendered valuable grazing grounds 
by digging up and burning every cadaver, by the thorough drain¬ 
age of the land so as to keep the height of the ground water at a 
low level and by keeping all animals off such land for two years, 
except those necessarily used to plough it up and expose it to the 
sun and air several times a year. In general, the dangerous lo¬ 
calities are small, and can be fenced in, and by simple lowering 
of the ground water can be rendered safe in two years. 
In order that a susceptible animal shall become infected with 
an infectious disease of this nature, it is necessary for it to be in 
