SIMPLE PNEUMONIA IN THE HORSE. 179 



"set" in the tissue, indicating small masses of exudate which have 

 been poured into the pulmonary alveoli, where they have coagulated 

 and become adherent to the walls of the air vesicles. Sections are 

 less smooth than at the former period ; they have a granular appear- 

 ance due to projection above the general surface of fibrinous coagula. 

 Moreover they no longer transude liquid, but on scraping yield small 

 quantities of blood-stained serosity, holding in suspension small 

 opaque whitish granules. One might be led to regard these modifica- 

 tions in appearance of the pulmonary tissue as indicating complete 

 disorganisation, but such is not the case. Microscopic examination 

 shows the following condition : — The air-cells are plugged by fibrous 

 clots containing leucocytes, red blood-corpuscles, epithelial cells, and 

 large migratory cells, exhibiting highly refractile granules ; in many 

 cases the epithelium is partly preserved ; many capillaries are oblite- 

 rated, but the alveolar ducts, though thickened and infiltrated, are 

 seldom much injured. 



In human pneumonia, pneumococci are almost invariably found in 

 the affected area, whatever the stage of the disease. The lesions of 

 simple lobar pneumonia in the horse contain various microbes, the 

 pathogenic action of which has yet to be demonstrated. 



When resolution occurs, the exudate contained in the air-cells is 

 freed, detached, and liquefied ; the resulting material, which is got rid 

 of through the bronchi, forms the discharge seen at this stage ; the 

 hypera^mia disappears, the alveolar ducts regain their normal cha- 

 racter ; the liquid which filtered into them becomes reabsorbed ; the 

 epithelium is restored at the points where it had been lost, and the 

 lung soon regains its function in an almost perfect degree. 



The post-inoytcin examination of patients dead of pneumonia some- 

 times reveals generalised pulmonary congestion, pleurisy, or myo- 

 carditis, sometimes purulent or gangrenous centres in the hepatised 

 tissue. 



Pulmonary suppuration assumes several forms ; in certain cases 

 small abscesses are found scattered throughout a mass of hepatised 

 tissue ; in others there are present one or more large abscesses, which 

 usually communicate with large bronchi. The contained pus is 

 whitish, creamy, and odourless, or reddish in colour, resembling wine 

 lees, and offensive. 



Gangrene is oftenest represented by little greyish-yellow tracts 

 scattered through the hepatised part. Sometimes it is " massive," 

 and affects a large portion of the diseased lobe ; it may assume various 

 appearances, the dead tissue being soft, blackish, violet, greenish grey, 

 or reduced to the condition of a granular mass. Tiie periphery of 



