PNEUMONIA. INFLAMMATION OF THE LUNGS. 271 



sity 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 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 impervious where no air passes no sound will be heard, 

 not even the natural murmur. 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. If there is considerable inflammation or tendency to 

 congestion, the crepitating, crackling sound will be recognized, and in propor- 

 tion 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 com- 

 mits in the very centre of the rib-cased cavity of the body." 



A horse with any portion of the lungs hepatized cannot be sound. He can- 

 not be capable of continued extra exertion. His imperfect and mutilated lung 

 cannot supply the arterialized 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 the 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. It occupies a space that should be employed in the function of 

 respiration, and by its pressure it irritates the neighbouring parts, and exposes 

 them to inflammation. 



By and by, however, another process, never sufficiently explained, commences. 

 The tubercle begins to soften at its centre, a process 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. The pus increases ; the cyst becomes 

 more and more distended ; it encroaches on the substance of the lungs ; it comes 

 into contact with other tubercles, and the walls opposed to each other are 

 absorbed by their mutual pressure ; they run together, and form one cyst, or 

 regular excavation, and this sometimes proceeds until a considerable portion of 

 the lung is, as it were, hollowed out. By and by, however, the vomica presses 

 upon some bronchial passage ; the cyst gives way, and the purulent contents 

 are poured into the bronchige, and got rid of by the act of coughing. At other 

 times the quantity is too great to be thus disposed of, and the animal is suffo- 

 cated. Occasionally it will break through the pleuritic covering of the lung, 

 and pour its contents into the thorax. 



Abscesses may exist in the Lungs undiscovered. It is scarcely conceivable 

 to what extent they sometimes exist in animals of slow work, without 

 being detected by the usual means of examination. Mr. Hales says that he 

 gave a physic ball to a cart-mare with a bad foot, and she soon afterwards died 

 suddenly. When inquiring as to the cause of death, he was told, and not very 

 good-humourcdly, that his physic had killed her. He asked, if it had purged 

 her violently ? " No !" it was replied, " it had not operated at all." She was 



