ANATOMICAL CHARACTERS. 531 



selves in ca piinctiform or radiated manner over patches of 

 the membrane, the endothehum of which is still intact. 

 Very often these newly appearing bloodvessels occur as a 

 number of spots or streaks slightly elevated, and, steadily 

 extending, at length by coalescence give to the membrane 

 the appearance of a uniform redness more or less extensive. 



In all, save the mildest forms of pleuritic inflammation, the 

 first effect upon the membrane, in addition to turgescence, is 

 probably a state of dryness. Very shortly this suspension of 

 secretion is succeeded by an increased exudation of serous 

 fluid, containing more or less plastic and organizable material, 

 the true product of inflammatory action ; with the effusion of 

 this liquor sanguinis we have also an emigration or passage 

 from the inflamed vessels of the corpuscular elements of the 

 blood. With this activity and change in the vascular struc- 

 tures we have certain alterations occurring in the membrane 

 itself; the endothelial cells enlarge, multiply, rupture, and 

 are shed, and these, mingling with older cell-elements, become 

 mixed with the exuded fluid in the pleural sac. The effect 

 of these activities and changes is to give to the pleural 

 membrane a roughened vascular appearance, very unlike 

 its natural smooth and glistening character. This surface 

 rapidly becomes coated with a layer of fibrinous material 

 of a soft, velvety, or reticulated character, from which fluid 

 continues to exude. This condition, when occurring over the 

 opposing surfaces of the sac, may, if liquid does not inter- 

 vene, produce adhesion of the formerly separated membranes ; 

 or even when the fluid is not in great quantity, give rise to 

 feeble attachments. In some instances there may be little 

 exuded fibrinous material present ; but union may occur from 

 the interconnection of the raised and papillated growths of the 

 sub-endothelial tissue. 



The eftused material contained in the pleural sac is of 

 variable amount, and at first is always turbid, from the quantity 

 of emigrant leucocytes and endothelial cell-elements which 

 probably proliferate in the eftused material. AVlien the in- 

 flammatory action is both severe and extensive, or Avhen the 

 amount of fluid in the cavity is great, so keeping separate the 

 membrane covering the walls of the chest and the surface of 

 the viscera, union will not ensue until the action somewhat 



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