592 SPOEADIC DISEASES. 



2. Absence of sound in the inferior part of the thorax, reaching 

 to a certain line, above which the respiratory sounds are heard. 



As the fluid accumulates, the absence of sound ascends. In 

 some cases of hydrothorax one or two other sounds are heard, 

 namely, metallic tinkling, and a gurgling or splashing sound. 

 These sounds are only heard when gas or air and fluid coexist 

 in the pleural cavity. The metallic tinkles may occur from 

 drops of fluid, imprisoned in false membranes, falling from the 

 roof of the pleural cavity into the liquid beneath, or may result 

 from the bursting of bubbles of air or gas on the surface of 

 the liquid. 



In the horse the pleural sounds are less distinct than in the 

 ox and dog. 



The sounds termed bronchophony, pectoriloquy, a^gophony, 

 and amphoric resonance, produced by modifications of the voice 

 during articulation, do not apply to any morbid sounds heard 

 in the lower animals. 



CARDIAC SOUNDS. 



If the ear or stethoscope be applied to the lower part of the 

 shoulder or arm, or if the left (near) fore leg be extended, and 

 the humerus pulled forward as far as possible, the sounds of the 

 heart can be made put. 



The sounds of the heart in health are two in number : first, a 

 longish, dull sound, then a sharp sound, succeeded by a pause, 

 and then the recurrence of the sounds in a regular and uniform 

 manner, provided the animal is not excited nor in any way dis- 

 turbed. The first sound coincides with the hardening of the 

 ventricles, the complete closure of the auriculo-ventricular valves, 

 and the opening of the arterial orifices ; is caused principally 

 by the sudden distension of the ventricles, and is of the same 

 nature as the noise made by all muscles in contracting against 

 a resistance. 



The second sound is undoubtedly due to the sudden closure 

 of the sigmoid (semilunar) valves at the conclusion of the ventri- 

 cular contraction. This has been proved by experiments on 

 living animals, the sound being destroyed by hooking back the 

 semilunar valves. 



The impulse of the heart may be felt by placing the hand 

 directly upon the left side of the chest, immediately behind the 

 elbow. It is very distinct in flat-sided and lean animals, less 



