686 ON THE CAVITY OF THE THORAX IN THE HORSE. 
shorter time, even though there exist voluminous caverns. 
This is especially the case when the caverns are filled with 
solid matter, or when the bronchial tube communicating with 
it is obstructed. But this absence of cavernous sounds 
ceases from the moment the contents are expelled, through 
some provoked cough. 
Acute tuberculisation of the lung yields different physical 
signs. Auscultation gathers sounds of catarrh, or of the first 
stage of pneumonia. When there exists tuberculous infiltra- 
tion, the indications are similar to those furnished by acute 
pneumonia in the third stage. 
Signs of Pleuritic Exudation. — In this affection the 
differential diagnostic is especially important, and is not 
less difficult to establish than that of the preceding disease. 
Very small quantities of pleuritic serosity do not admit 
of recognition by physical indications. A considerable hy- 
drothorax even is difficult of detection, unless it be accom- 
panied by a plastic layer, at least an inch in thickness, upon 
the external surface of the lungs, and providing these last are 
not filled with air. The diagnostic also is but conjectural, 
when, as often happens, there is present pleuro-pneumonia. 
When exudation is present in very large quantity, in such 
manner that the liquid produces compression upon the dia- 
phragm and lungs, physical inquiries admit of a certain 
diagnosis, although often the morbid modifications appear 
greater at the autopsy than one had supposed them to be 
during the life of the animal. The upper part of the thorax 
yields to percussion a clearer, and more elevated, and a tym- 
panitic sound : lower down the sound becomes void and flat. 
Exudation never mounts so high as the upper part of the 
lung. When it has risen to cover half of the lung, it pro- 
duces death. Auscultation proclaims at the superior parts of 
the lungs an indeterminate respiration. Towards the middle, 
the respiration becomes bronchial, while in the inferior region 
we have nothing but the respiratory murmur. 
A characteristic symptom of pleurisy is the rubbing sound : 
this is the certain sign of a plastic exudation upon the free 
surfaces of the pleurae. Nevertheless, it is not often that we 
discover this rubbing sound in the horse ; one only hears it dis- 
tinctly at the commencement or towards the termination of 
the disease, when the pleurisy is simple, or when it is com- 
plicated with pneumonia. Naturally, the appearances pro- 
duced, and the pathological changes of the exudation itself, 
will vary more or less, according to the presence or absence 
of adhesions, encystements, and pneumo-thorax. 
We never can be sure about pleuritic exudation of little 
