PHYSICAL SIGNS OBTAINED BY PERCUSSION. 429 



8. Variations of Intensity or Force of the General Movements. — 

 («) These may be in excess, the animal breathing deeply and 

 with greater force, more air being changed durmg each respira- 

 tion ; (6) they may be deficient in force and intensity, less air 

 being changed during an individual respiration. Both these 

 conditions are observed in diseases of the lungs themselves. 



4. Disturbance in the Rhythm of the Respiratory Act. — The 

 chief abnormality here is the prolongation or shortening of 

 either the inspiratory or expiratory movement. The exercise 

 of palpation itself is also useful in aiding us, through the 

 development of local pain on pressure, in diagnosing diseased 

 conditions of the pleurae and thoracic walls. 



II. PHYSICAL SIGNS OBTAINED BY PERCUSSION. 



A. Normal Percussion Sounds. — Over the anterior portion of 

 the air-passages, the sinuses of the head, we find that percus- 

 sion elicits sounds varying with the age of the horse and 

 development of these cavities. In the young, where the 

 amount of bone tissue is largely preponderating, and the cavities 

 comparatively small, the sound is hard and non-resonant; 

 as the cavities become enlarged, the walls thinner, with the 

 quantity of contained air increased, the sound is full, and 

 resonance augmented. 



In health, over the thoracic walls there are encountered 

 considerable variations in percussive sounds. Where the chest 

 is least clothed with soft tissue, and where the lung-structure 

 is in immediate contact with the thoracic walls, a moderately 

 clear sound is elicited ; the sound depending upon the air, or 

 rather upon the vibration of the air contained in the pulmonary 

 tissue, and the vibration of the walls of the chest. This sound 

 varies both with the amount of air contained in the pulmonary 

 tissue, and with the force employed in percussing. When 

 little force is emj)loyed the sound is low, though clear ; when 

 the force is greater the sound developed is harder, and if the 

 part struck is over any considerable tract of pulmonary 

 structure rather resonant. When the animal is in a recumbent 

 position the sound is distinctly harder and more resonant than 

 when standing. 



In endeavouring to carry out this means of exploring the 

 chest in our patients it requires us to remember the relative 



