Report on the Pathological Anatomy of Pleuro-pneumonia. 197 
•the stage of development of the pleuiitis, and never with the 
disease of the lung. I am convinced that the lung disease usually 
exists for months without being suspected, and invariably the 
beast is first thought to be sick only when the affection has 
spread to the pleura, and caused intense inflammation of that 
membrane with its accompanying well-marked symptoms. And 
I believe that if our diagnostic powers were improved, cases of 
pleuro-pneumonia without pleurisy would more frequently be 
met with. 
In thus asserting that the pleural lesion is secondary to that of 
the lung, I do not mean to imply that the lung parenchyma 
cannot under any circumstances become secondarily affected 
from the pleura covering it. It will presently be seen that 
nothing is more common than this spreading of the disease 
from the pleura to the subjacent tissue. It can be seen in every 
case where the inflammation of the pleura is severe, and has 
lasted some little time. The infective process may be commu- 
nicated from the primarily affected lobe to its neighbours, by 
means of the intervention of the pleura, and in these cases the 
pleura does seem to be the starting-point of the processes in the 
lobes, which are thus secondarily engaged. But if the primarily 
affected lobe be carefully examined, it will always be found to 
contain a wedge of typical marbling, extending towards the root 
of the lung, with the bronchi and vessels diseased in the manner 
already described. In this deep-seated, conical, indurated region, 
the morbid process is more developed than elsewhere. And it 
is such a centre, I believe, that forms invariably the original 
point of disease. One such focus, at least, can always be found 
in some part or other of a diseased lung, no matter how exten- 
sive the wide-spread shallow pleural infection may be. To me 
it seems impossible to explain this chronic, old, indurated part 
of the lung disease as a result of the acute, recent pleurisy. 
On the other hand, there is no difficulty in explaining the 
pleuritis as a result of the lung lesion. In many of the cases 
slaughtered immediately after the development of the pleural 
inflammation, this relationship is most obvious. Putting aside 
the existence of any specific form of infective material, the 
irritation and inflammation of the pleura may be explained by 
the mere mechanical injuries done to the membrane by the 
swelling of the subjacent lung during the disease. To this 
exciting cause may be added defective lymph drainage and im- 
paired blood supply. 
In the cases where the pleural disease is associated with 
haemorrhagic infarction — and these are remarkably common — of 
course there can be no difficulty in explaining the pleuritis. 
The pleura may be torn ; sOme blood may escape into its cavity 
