286 PNEUMONIA. — INFLAMMATION OF THE LUNGS. 



auscultation. Here again is tlie advantage of being perfectly acquainted 

 witli the deep distant murmur presented by 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 will make himself best acquainted 

 ■with the respiratory murmur in its full state of development. He should 

 next take an older and somewhat fatter horse ; he will there recog-nise the 

 same sound, but fainter, more distant. In still older animals, there will 

 sometimes be a little difficulty in detecting it at all. Repeated experi- 

 ments of this kind will gradually teach the examiner what kind of healthy 

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

 thus he "vvill be better able 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 mistaken. Its loudness and perfect 

 character will characterise 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 por- 

 tions or patches of it in which the inflammation is so intense as to produce 

 congestion and hepatisation. Enough remains either unaffected, or yet 

 pervious for the function of respiration to be performed, and the animal 

 lingers on, or perhaps recovers. By careful examination with the ear, 

 this also may be ascertained. Where the lung is imper\'ious — where no 

 air passes — no sound will be heard, not even the natural murmur. Around 

 it the murmur will be heard, and loudly. It vnll be a kind of rushing 

 sound ; for the same quantity of blood must be arterialised, and the air 

 must pass more rapidly and forcibly through the remaining tubes. If 

 there is considerable inflammation and tendency to congestion, the crepi- 

 tating, crackling sound will be recognised, and in proportion to the 

 intensity of the inflammation. The advantages to be derived from the 

 study of auscultation are not overrated. It was strong language lately 

 applied by an able critic to the use of auscultation, that ' it converts the 

 organ of hearing into an organ of vision, enabling the listener to observe, 

 with the clearness of ocular demonstration, the ravages which disease 

 occasionally commits in the very centre of the rib-cased cavity of the body.' 



A horse with any portion of the lungs hepatised cannot be sound. Ha 

 cannot be capable of continued extra exertion. His imperfect and muti- 

 lated lung cannot supply the arterialised blood which long continued and 

 rapid progression requires, and that portion which is compelled to do the 

 work of the whole lung must be exposed to injury and inflammation from 

 many a cause that would otherwise be harmless. 



Another consequence of inflammation of tlie substance of the lungs is 

 the formation of tubercles. A greater or smaller number of distinct cysts 

 are formed — cells into which some fluid is poured in the progress of 

 inflammation : these vary in size from a pin's point to a large egg. By 

 degrees the fluid becomes concrete ; and so it continues for a while — the 

 consequence and the source of inflammation ; this constitutes a tubercle. 

 It occupies a space that should be emplo^^ed in the function of respiration, 

 and by its pressure it irritates the neighbouring parts, and disposes them 

 to inflammation. 



By and by, however, another process, never sufiiciently explained, com- 

 mences. The tubercle begins to soften at its centre, — a pr(M!HKS of 

 suppuration is set up, and proceeds until the contents of the cyst become 

 again fluid, but of a different character, for they now consist of pus. 

 This smooth defined collection of matter is called a vomica. The 



