THE MICROBE OF PLEURO-PNEUMONIA. 
233 
'of pulmonary serosity in the cellular tissue of the caudal ex¬ 
tremity of the animal to be immunized. But this serosity alters 
with great rapidity; it rapidly becomes putrid and loses its 
virulency, consequently a fresh lung is necessary for inocula¬ 
tion ; ordinarily a pleuro-pneumonic animal is killed at the mo¬ 
ment of the operation ; but, sometimes the destroyed animal has 
only an old lesion, where the serous exudate may have lost its 
virulency or where it may be entirely absent; at times, also, 
when essentially preventive inoculations are to be made, a 
pleuro-pneumonic cow to be killed cannot always be found. 
A real progress was reached when Pasteur taught us how to 
collect pure serosity from the connective tissue of the pleuro- 
pneumonic lung and also to obtain large quantities of virulent 
serosity by the inoculation in a forbidden region of a calf with 
a drop of pulmonary serosity. Then it became possible to make 
collections of virus and to distribute them far away, here and 
there, as it was needed. 
Yet the problem was not entirely solved ; pleuro-pneumonia 
serosity, even if gathered pure, loses its virulency somewhat 
quickly ; after one month, six weeks at most, inoculation re¬ 
mains ordinarily without effects. To be sure of being able to 
supply all demands, centres of production of virus mmst be es¬ 
tablished, where every month, at least, fresh subjects shall be 
inoculated. This is done at great cost in a small number of 
places. 
To determine the specific agent of the pleuro-pneumonic 
virus, to separate and cultivate it, would constitute, then, an 
immense progress. Unfortunately all those that have tried— 
-and they form a legion—have failed. 
We also have made numerous attempts, and that for a long 
time. They have always been fruitless. When it has been 
collected pure, in the perilobular sub-pleural lymphatic sacs, 
the most virulent pleuro-pneumonic serosity can be inoculated 
in all the nsital medias^ in air or vacuum, without ever giving 
culture. Neither can anyone succeed in coloring in them any 
microbic element with the use of any of the means known. 
