Aaite Croupous Pneumonia. Pneumonitis in the Horse. 225 



retains a measure of its softness, elasticity and permeability to air, 

 though it is considerably firmer and less permeable than that 

 which is in a state of congestion and differs further from it in 

 exuding from its cut surface not a grumous, dark bloody pulp, 

 but a clear straw colored fluid. In the advanced red hepatisation 

 the lung is of a firm consistency and granular liver like appear- 

 ance. In color it varies from a bright red to a dark liver hue, 

 the darker shades being chiefly met with in old animals or when 

 the inflammation and fever have been intense and prostrating. 

 Varying shades are seen in different lobules of the same lung. 

 Its air cells are no longer pervious, it no longer crepitates under 

 the pressure of the finger, nor floats in water, and its friability is 

 such that it breaks down readily when the finger is thrust into its 

 substance. Its surface is distinctly granular from the fibrinous 

 plugging of the alveoli. Such a lung does not collapse when the 

 chest is opened but retains its bulk and shape and in some cases 

 the diseased portion may, by reason of the abundance of the ex- 

 udation, be really larger than the same portion of lung in a normal 

 state of dilatation. Its surface may thus retain the imprint of the 

 ribs. Owing to the stasis of the blood in the vessels a hepatised 

 portion of lung cannot be injected. The exudation which infilr, 

 trates the lung tissue and obliterates the air cells contains iij the 

 vicinity of the bloodvessels numerous granular masses and cor- 

 puscles and in the darker colored portions blood globules, owing 

 to the action of diapedesisofthe red cells and the rupture of minute 

 vessels. The smaller bronchial tubes stand out white and empty 

 showing that they have escaped the inflammatory action. He- 

 patization usually extends from the anterior lobe or lower border 

 upward. 



Gray hepatization is a sequel of the red and presents the same 

 firmness, friability and usually the same granular aspect ; the 

 lack of crepitation on pressure, and the higher density than water. 

 From the cut surface a fatty or purulent fluid exudes spon- 

 taneously, or in other cases only when pressure is applied. The 

 granular masses and corpuscles have disappeared, and if supura- 

 tion is not so abundant as to prove extensively destructive to 

 lung tissue, that is gradually cleared up and restored to health. 

 This state is always a very perilous one. 



Abscess of the lung sometimes met with in animals dying of 



15 



