NEW RESEARCHES UPON PLEUROPNEUMONIA, ETC. 
500 
NEW RESEARCHES UPON PLEURO PNEUMONIA AND 
ITS PREVENTIVE INOCULATION. 
By Dr. Willems. 
(Continued from page 464.) 
In concluding, I propose to present the Academy with my 
views upon the etiology of exudative pleuro-pneumonia. 
This disease is of a virulent character ; this is universally ad¬ 
mitted. 
But what is a virus ? It is a mysterious entity, whose essen¬ 
tial constitution is as little known as that of electricity ; its ulti¬ 
mate character is revealed only by its effects, and its constitution 
still escapes our investigations. But it is to be hoped that a day 
will come when, with our powerful means of investigation, we 
shall succeed in fully enlightening ourselves, and be justified in 
placing greater numbers of virulent diseases in the class of para¬ 
sitic affections. 
Transmissible or contagious diseases, or those which are trans¬ 
mitted from a diseased to a healthy organism, may be divided into 
two classes—first, the virulent diseases; that is, those which are 
transmitted by a contagium whose nature is yet unknown; and 
again the parasitic diseases, whose agents of transmission have 
been known during various periods of time, such as scabies 
(acarus), ring-worm (trychophyton), trichinosis (trichina), foot 
and mouth disease (oidium). 
After these, thanks to the recent discoveries of Davaine and 
Pasteur, we find, anthrax (bacteridie), septicemia (septic vibrio), 
and chicken cholera. 
The diseases of this second class are at the present time well 
known, and consequently can no longer be ranked amongst the 
virulent diseases; microscopic studies have revealed their nature, 
and brought to our view as agents of contagion, the germ-cor¬ 
puscle and the parasite, animal or vegetable, which can be repro- 
