PHYSICAL SIGXS OBTAINED BY PERCUSSIOX. 431 



ever, be detected over the eighth, but agam dechnes, and is 

 replaced by didness over the twelfth or thirteenth rib. 



B. Abnormal Percussion Sounds. — In abnormal conditions of 

 the thorax and contamed organs the resonance, as elicited by 

 percussion, becomes variously modified. It may be (1) aug- 

 mented, (2) diminished, (3) lost. 



1. Increased or augmented percussive sound — change in its 

 character — may be general or partial. It is general in cases of 

 extreme pulmonary emphysema, from the amount of air con- 

 tained in the interlobular structures, and often occurring in 

 quantity in the sub-pleural tissue. Partial increase of sound 

 may follow obstruction, whether from solidification or compres- 

 sion of portions of the lungs, the unaffected being compelled to 

 take in a greater amount of air than natural in dischardno- 



. ... o o 



extra functional activity, in this way increasing the natural 

 cellular capacity, becoming more dilated, and consequently 

 more resonant on percussion. 



2. Diminished resonance, as a continuous state, I have not 

 met with in the horse to any extent, as it is generally so quicldy 

 followed by loss of sound. It may, however, occur from any 

 cause which partially obstructs the entrance of the air into the 

 air-sacs, as liquid effusion in the interlobular connective-tissue, 

 or the dissemination through the pulmonary structures of 

 certain diseased products. 



3. Loss of resonance in the pulmonary tissue is never entire; 

 and its partial or local annihilation may be due to hepatization 

 or to effusion in the plem-al sac. When due to the former, 

 the loss of sound will probably have been preceded by the 

 ' crepitation ' indicative of inflammatory action. When accom- 

 panying the latter, we may have observed symptoms indicative 

 of pleuritis ; while in the horse this loss of percussive sound is 

 likely to exist on both sides, beginning at the inferior part of 

 the chest. 



III. PHYSICAL SIGXS DRAWX FROM AUSCULTATION. 



A. Normal Respiratory Sounds. — In health, auscultation over 

 the extended air-passages in the horse discloses at least three 

 typical sounds : 



1. Tracheal, Laryngeal,or Nasal. — This is the sound common 

 to the large air-cavities of the head, the lar^mx, and the great 



