1889.] Etiological Classification of Diseases. 959 
Speaking in the old sense, such a disease would be "contagious." 
Speaking acccording to the nonsensical usage of that word at 
present, no one can tell what its true origin might have been. 
In contradiction to his obligatory parasitic diseases, Hueppe 
has given us the term of " faculative parasites," by which he 
means to indicate diseases of parasitic origin, but in which the 
focus of primary development (of the germs) is invariably outside 
the animal organism ; still, that they have the faculty of living, 
for a time, within the organism of certain species of animal life, 
becoming parasitic or disease-producing for the time, when such 
animal organisms offer the necessary nutrient conditions to their 
life. To this class Pettenkofer has given the name of " exoge- 
nous," while I have termed them "extra-organismal," or diseases 
which found their primary origin in internal or surrounding con- 
ditions ; or, in other words : 
An exogenous disease is one which invariably finds its locus 
of primary origin not in, but outside of, 
that is, in the earth, or in the surroundings 
Its micro-organismal cause develops under certai 
climate and soil which offer the necessary nutr 
and continuous development. 
The infected earth or locality bears the same relation to animal 
hfe in the origin of exogenous disease that the infected afiimal 
organism does to healthy susceptible animals in endogenous dis- 
eases. That is, they each form centres of primary origin in their 
relation to specific diseases in their respective class, but with this 
difference : the focus of primary generation, or infection, is fixed 
in exogenous diseases, while it is movable in endogenous. 
The locus infectionis, that is the point of primary infection or 
origin, is contagious in either case. In the one a healthy sus- 
ceptible individual must come in direct contact, be upon or in 
such an infected locality, or come in. contact with material derived 
directly from such a locality ; while in an endogenous disease the 
same occurrences must take place in reference to some form of 
animal life. Hence it is to be readily seen that the word con- 
tagious has no logical use or place in the nosology of diseases, 
according to the results of modern investigation. Yet we find 
il life, where 
conditions of 
