202 Report on the Pathological Anatomy of Pleuro-pneumonia. 
seems more extensively diseased than any other structure, in the 
very early stages of the affection. 
From this it would appear that the irritation of the peri- 
bronchial lymph-channels is produced by a form of chronic 
inflammation in the structure of the bronchial wall, which is 
brought about by the disease of the mucous membrane. 
So constantly have I met with this condition in the opaque 
parts, that I have but little hesitation in affirming that the disease 
commences in the air-passages as a chronic inflammation, asso- 
ciated Avith destruction of the bronchial mucous membrane. 
I cannot say what is the exact size of the tubes in which the 
inflammation begins ; it seems likely that the lobular bronchi 
are those most readily affected, and certainly the very small 
tubes are invariably attacked, even when the disease is in its 
most recent stage. The impression left on my mind is, that 
,the delicate lobular bronchi are those first attacked in the 
majority of cases, though often the morbid processes are more 
striking in those tubes about the size of a quill. 
As to the immediate exciting cause of this strange form of 
bronchitis, little can be said. No light is thrown on the subject 
by the morbid anatomy, no constant specific elements have 
been found in the affected part. The aetiology of the disease 
must be studied clinically and experimentally. The only 
suggestion I should presume to make upon this subject is a plain 
deduction from the reading of the pathological events as I have 
traced them out : it is this, that pleuro-pneumonia being a local 
disease, starting in the bronchial mucous membrane, it can only 
be produced by direct and immediate infection of that mem- 
brane, and it is little to be wondered at that inoculation of the 
tail, or other part, cannot produce the local disease in the lung, 
though it may set up, in the part operated upon, a form of 
progressively infective inflammation, which runs a course not 
unlike that of the lesion of the lung. I have had many oppor- 
tunities of satisfying myself that when a tail is " successfully " 
inoculated the subcutaneous connective tissue undergoes a 
change exactly like that between the lobules of the lung, and the 
infective process rapidly spreads by the lymphatics. 
I can well understand how a beast, by sniffing the fodder of a 
diseased neighbour, m<ay draw into its air-passages some of the 
dried discharge, and thus infect its bronchial mucous membrane 
and get pleuro-pneumonia, while all the skill science can apply 
will not induce the disease of the lung by mediate contagion, i.e. 
the inoculation or injection under the skin or into the vessels 
of infective material procured from a diseased lung. 
Whether there be any special virus which acts as the specific 
cause of this disease or not, must also be left to experimental 
