534 PEKCUSSION. 



diminution of resonance may result in the ox, from the 

 presence beneath the costal pleura of an extensive tubercu- 

 lous deposit, or from an extended formation of false membrane 

 over the sama The former may often be distinguished from 

 the latter, by its being accompanied or preceded by a 

 distinct friction sound, audible on auscultation. A third 

 cause of general diminished resonance, is a uniform deposit 

 throughout the lungs of cancerous, or other abnormal mate- 

 rial The causes of partially diminished resonance are : a 

 circumscribed false membrane on the pleurae, or the infiltra- 

 tion of the pulmonary tissue by some liquid, which only 

 partially prevents the entrance of air into the air sacs. 

 There may likewise be hepatisation of a small portion of 

 lung tissue, but this is readily distinguished from the causes 

 previously mentioned, by the presence of a crepitant rale 

 round the hepatised portion. 



Absence of resonance is never observed over all parts of the 

 chest at the same time. It is necessarily circumscribed, and 

 is usually due either to hepatisation of lung tissue, or the 

 effusion of liquid into the pleural cavities. If from hepatisa- 

 tion, it will not probably occur in the lower region of the 

 chest, or over the whole of that region, the progress of the 

 dulness will be preceded by a crepitant rale, audible on 

 auscultation, and the resonance and respiratory murmur will 

 be slightly increased on the same part of the opposite lung. 

 If dulness results from effusion, the history of the case will 

 indicate that pleurisy has existed, and has become suddenly 

 relieved, friction sounds will have preceded the dulness, 

 pain is felt on pressing the intercostal spaces, and, in the case 

 of the horse, the dulness will exist equally upon both sides. 

 In the ox, fluid may exist in one side only of the pleurae, and 

 the last statement accordingly does not hold good in this 

 animal. The same remark applies to the smaller classes of 



