ANATOMICAL CHARACTERS. 495 



4. The existence of other diseased conditions, (a) Probably 

 the most fertile source of pneumonia in the horse is that of 

 neglected or badly treated ordinary catarrh. Here the 

 inflamed condition of the mucous membrane is very apt to 

 extend downwards, implicating the smaller air-tubes ; while 

 succeeding bronchitis Ave most commonly, in such cases, have 

 pneumonia also. This disposition of catarrhal inflammation 

 to extend from the upper to the lower air-passages is often 

 seen when the animals are comfortably housed and well taken 

 care of, but is nearly sure to folloAv when in ordinary catarrh 

 the animal is in any manner abused or otherwise circumstanced 

 so as to favour the development of pneumonia, (b) Following 

 some specific and general diseases, also certain states of blood- 

 contamination. In this form of secondary or complementary 

 pneumonia there are many instances where accompanying, or 

 probably immediately inducing, the inflammatory condition 

 is pulmonary thrombosis ; this is well exemplified in the 

 pyasmic state accompanying specific arthritis and other septic 

 and infective conditions. 



5. Epizootic agencies. Pneumonia may of itself, or as f)art 

 of the symptoms or development of such epizootics as influenza, 

 call for special attention, where by Avhatever channel the in- 

 ducing factor — the so-called epizootic influence or agent — may 

 enter the system, it is so far occult or inappreciable that it 

 is only known by its action and the results which it may 

 mduce. 



Anatomical Characters. — The general pathological condition 

 of pneumonia may be stated as hyperemia and osdema of 

 lung-tissue, with a variably constituted fibrinous exudation, 

 chiefly in the air-cells and minute bronchi. These conditions 

 of vascular turgescence and exudation are, in the examination 

 of animals which have succumbed while thus affected, pre- 

 sented for observation under somewhat variable characters. 



Although it is probable that the very earliest condition of 

 lung-structure when about to become inflamed is that of 

 irritation or arterial injection, indicated by crepitation and 

 harsh respiration, and exhibiting a state of unnatural dryness 

 and a bright red colour, the usually observed appearance and 

 condition at the commencement of pneumonia is rather that 

 known as The stage of simple engorgement. 



