170 Report on the Pathological Anatomy of Pleura-pneumonia. 
There are, then, in studying the diseases of the lower animals, 
many difficulties which balance the one advantage, of which 
we often hear, namely, that of being able to kill the beast at any 
time, and thus find out the steps in the morbid changes which 
correspond to the A'arious stages of the disease. Practically, 
in the case with which I have to deal, this advantage is but 
little felt, for there is really no control over the time of 
slaughter, and there seems a clinical difficulty in ascertaining 
how long the disease has lasted, so that the exact stage it has 
reached cannot be known until the animal is killed. 
These difficulties doubtless explain the great paucity of 
scientific literature on this subject, and the complete want of any 
adequate scientific explanation of the progress of the disease. 
The following references may suffice to give some idea of the 
present standpoint of our knowledge of the subject. 
The first accurate description of the morbid anatomy of pleuro- 
pneumonia that I have been able to find, is given by F. Weber,* 
and, as far as the description of the appearances of the diseased 
lungs is concerned, this paper has not been surpassed by any since 
published, that I know of. He calls the disease interlobular 
pneumonia, and attempts to explain its development as a form 
of chronic inflammation of the tissues between the lobules. 
Though he recognised that there were different kinds of conso- 
lidation, he appears only to have submitted one of these varieties 
to minute investigation, otherwise his clear reasoning would not 
have led him to the conclusions which he announces in his paper. 
He says that examination of the diseased lung gives two 
negative results : — 
1. There is no trace of croupous exudation in either the large 
or small bronchi ; the mucous membrane in the larger ones is 
perfectly healthy ; in the smaller tubes a mere trace of catarrhal 
injection can be detected. 
2. In the lung tissue itself the air cells are filled with fluid 
as in oedema, and not with solid exudation. 
From these results he concludes that the tissue of the lung is 
in a state of oedema, not hepatisation. 
With reference to the starting-point of the disease, he says, 
" I now pass to the beginning stages, which give the clearest 
proof that the interlobular connective tissue, and the pleura, are 
the real seat of the disease." The other parts, he thinks, become 
secondarily affected, the exudation causing a kind of strangu- 
lation of the lobules, which gives rise to hypera?mia, pulmonary 
apoplexy, serous infiltration, and (very rarely) hepatisation. 
The connective tissue of the lung, then, he considers to be "the 
* Virchow's Archiv., Bd. vi. p. 89. 
