Report on the Patholoffical Anatomy of Pleuro-pneumonia. 203 
inquiry to determine positively. I have searched in vain for a 
morphological element which could be regarded as the materia 
jieccans. However, the general aspect of the morbid processes 
gives one the idea that some peculiar infective product is at 
work. In very many cases foreign elements, so peculiar as to 
provoke suspicion, have been found, but further investigation 
failed to bring home to them the necessary pathogenic pro- 
perties, as they have generally proved to be inconstant or 
harmless substances, whose presence is either accidental or un- 
important. 
The fact that no morphological representative of an infective 
material can be found, is no proof that it does not exist. How 
long is the list of diseases which are acknowledged on all sides 
to depend on the presence of a peculiar virus ? How very few 
— if there be any — of these specific materials do we know in 
any other way than by the effects they produce? Some, we 
know, cause a general affection of the blood, some a peculiar 
primary local lesion, and subsequent general infection, others 
again give rise to a purely local inflammation with a specific 
character. In the latter category I am inclined to place the 
virus of pleuro-pneumonia. When applied to the bronchial 
mucous membrane or introduced into any lymph-bearing tissue, 
it sets up chronic inflammatory changes associated with ex- 
cessive exudation. Ordinary inoculation illustrates this per- 
fectly. The operation causes practically no inflammation ; but 
after a definite period of incubation, varying from ten to fourteen 
days, a local specific inflammation is produced in the connective 
tissue ; but this is not accompanied by any constitutional dis- 
turbance, except when it spreads extensively : timely amputa- 
tion of the tail, however, usually prevents this unfortunate 
accident, and the animal quickly recovers without having any 
traces of a blood-disease. 
I abstain from attempting to discuss the many abstract 
questions or theories which have from time to time been intro- 
duced into the study of this peculiar affection. Whether it be 
real inflammation, or some mysterious specific change differing 
from all other diseases ; whether it be comparable with any 
human disorder ; whether it be zymotic or not, &c. These are 
very interesting speculations, but their consideration is not very 
likely to lead to any immediate practical result ; and therefore 
it appears to me more profitable to attempt to unravel the 
intricate sequence of pathological events, and trace the succes- 
sive steps of the morbid changes which occur in pleuro-pneu- 
monia, for I am satisfied that it is along this track we must 
travel, if we hope ever to arrive at the true pathogeny of the 
disease. 
