508 ANALYSIS OF CONTINENTAL JOURNALS. 
and animals, causing more or less marked pathological 
ravages. That certain virulent maladies predispose to para¬ 
sitism is another question which we shall examine, because its 
discussion forms part of our programme. That between the 
pathological action of the parasitic proto-organisms, and that 
of the agents to which we will attribute the cause of virulence, 
there are certain analogies, shall be shown in the comparisons 
which will often be made. That it is, at present, rash to 
affirm that the progress of science will not one day show in 
these analogies characters of identity I am the first to admit; 
but, in the meantime, that this identification should be 
accepted as a proved fact, or even as a simple probable fact, 
you will unhesitatingly deny wheti you shall have followed 
me in the experimental demonstrations that I am about to 
offer you. 
The contagious maladies which have not parasitism for cause 
and means of transmission—such is , then , the domain of the viru¬ 
lent maladies, properly so called. It is in this domain that we 
will exclusively take the examples and the facts which we 
require for our study. And in order that we be not deceived, 
we shall leave on one side all the diseases situated on the 
frontier of this domain, and as to whose exact place there 
may be doubt or uncertainty. On this point the greatest 
reserve is imperiously demanded; for it must not be for¬ 
gotten that the general domain of contagious maladies them¬ 
selves cannot be, at present, sharply defined. Let it be 
remembered that for certain diseases, which have been 
known from the remotest antiquity, contagiousness has only 
been fully accepted in our own days. Finally, do not over¬ 
look the fact that many affections have been alternately in¬ 
troduced into the list of contagious maladies and removed 
from it; that even now the question as to whether such a 
malady is or is not contagious gives rise to the most ani¬ 
mated discussions. Evidently all this uncertainty should 
disappear. The extension that the application of the experi¬ 
mental method to the study of these questions is destined to 
receive should, on this point, confer a rapid progress on 
science. 
By the way, we shall have occasion to indicate some of these 
diseases. But it is necessary to take things as they are, for 
such is the actual state of affairs that one is forced to make a 
limited choice of examples in the list of maladies whose 
theory we have to establish. We shall, therefore, only take 
sure examples, some borrowed from human, the others from 
veterinary pathology—the latter the most numerous, because 
they are better adapted for experimental demonstrations. 
