INFLAMMATION OF THE LUNGS. 189 



the healthy lung. This sound is most distinct in the young 

 horse, and especially if he is a little out of condition. On such 

 a horse the tyro should commence his study of the exploration of 

 the chest. There he Avill make himself best acquainted with 

 he respiratory murmur in its full state of development. He 

 should next take an older and somewhat fatter horse ; he will 

 there recognize the same sound, but fainter, more distant. In 

 still older animals, there will sometimes be a little difficulty in 

 detecting it at all. Repeated experiments of this Idnd will grad- 

 ually teach the examiner what kind of healthy murmur he should 

 expect from every horse that is presented to him, and thus he 

 will be better enabled to appreciate the different sounds exhibited 

 under disease. 



If pneumonia exists to any considerable degree, this murmur 

 is soon changed for, or mingled with, a curious crepitating 

 sound, which having been once heard, cannot afterwards be mis- 

 taken. It is caused by the infiltration of blood into the air-cells. 

 Its loudness and perfect character will characterize the intensity 

 of the disease, and the portion of the chest at which it can be 

 distinguished will indicate its extent. 



The whole lung, however, is not always affected, or there are 

 only portions or patches of it in which the inflammation is so 

 intense as to produce congestion and hepatization. Enough 

 remains either unaffected, or yet pervious tor the function of res- 

 piration to be performed, and the animal lingers on, or per- 

 haps recovers. By careful examination with the ear, this also 

 may be ascertained. Where the lung is impervious — where no 

 air passes — no sound will be heard, not even the natural mur- 

 mur. Around it the murmur will be heard, and loudly. It will 

 be a kind of rushing sound ; for the same quantity of blood must 

 be arterialized, and the air must pass more rapidly and forcibly 

 through the remaining tubes. 



A horse with any portion of the lungs hepatized camiot be 

 sound. He cannot be capable of continued extra exertion. 



Another consequence of inflammation of the substance of the 

 lungs is the formation of tubercles. A greater or smaller num- 

 ber of distinct cysts are formed — cells into which some fluid is 

 poured in the progress of uiflammation : these vary in size from 

 a pin's point to a large egg. By degrees the fluid becomes con- 

 crete or hardened ; and so it continues for a while — the conse- 

 quence and the source of inflammation. It occupies a space that 

 should be employed in the function of respiration, and by its 

 pressure it irritates the neighboring parts, and exposes them to 

 uiflammation. 



By and by, however, another process, never sufficiently ex 

 plained, commences. The tubercle begins to soften at its cen- 



