THE MICROBE OF PLEURO PNEUMONIA. 
239 
dare to be very affirmative. It will be only by a great number 
of experiments that this question of attenuation of the virus 
can be solved. 
As to the first point (preservation of the virulency by suc¬ 
cessive cultures in vitro)^ it is well established by the observa¬ 
tion of the cow No. 7, mentioned hereafter; this cow, inoculated 
Feb. 26, 1898, with 10 drops of a sixth culture, died March 19, 
with an enormous oedematous swelling, entirely alike those pro¬ 
duced by the inoculation of the most virulent pulmonary 
serosity. 
* 
* * 
The discovery of the agent of the plenro-pneumonic viru¬ 
lency does not only give the satisfaction of an overcome diffi¬ 
culty ; the result strikes higher. It gives the hope to succeed 
also in the study of such other virus whose microbe remains 
unknown to this day. 
What made the discovery of the microbe of pleuro-pneu- 
monia difficult was : first, its extreme small size ; second, and 
specially, the very peculiar conditions of its culture in artificial 
media. 
Is it not justifiable to suppose the existence of microbes 
:still smaller, while, instead of remaining within the limits of 
visibility, as it is for this one, are beyond them ; in other words, 
it can be admitted that there are microbes which are invisible 
to the eyes of man. 
Well ! even for those microbes, their study is yet possible, 
providing a media proper to their culture is found. Even then, 
in these attempts at cultivation, one will not be satisfied, to 
judge of his success or failure, with the changes which are 
present in the aspect or transparency of the media. The cul¬ 
ture of the microbe of pleuro-pneumonia is very rich ; still it 
only gives rise to a slight dubious aspect, a scarcely visible 
opacity in the fluid ; to be convinced of the reality of the cul¬ 
ture one must examine it comparatively with a tube of the 
.^ame bouillon not inoculated. Therefore, the possibility of a 
inicrobian culture without noticeable modifications in the 
