166 CONTAGIOUS DISEASES. 



degrade into lower forms of matter — i.e., caseous or calcareous — 

 and rarely to change to cicatricial tissue, and to remain latent 

 in the part for an indefinite period ; and that it may commence 

 primarily in the parenchyma of the lungs, and that finally the 

 tubular portion and vessels of the lungs become obliterated, not 

 only by the pressure of exudates external to them, but by histo- 

 logical elements and clots within them. In consequence of 

 these changes, the diseased lung becomes very heavy, sometimes 

 attaining the weight of twenty, thirty, or even fifty pounds, 

 sinks in water, is resistant, solid, non-crepitant, and on section 

 presents the marbled appearance already mentioned. 



In those rapid cases of death which occur aftet the first 

 introduction of the disease into a locality, the changes in the 

 lung tissue are those of an acute character; there is great red- 

 ness or blackness of the parenchyma — haemorrhagic infarction 

 — whidi is at same time loaded with much serosity, and is very 

 friable, soft, and easily broken by the finger ; but in the ex- 

 amples which most frequently fall under the pathologist's 

 notice the cadaveric lesions are — 1st. Extensive deposits of 

 yellowish, friable layers of false membrane upon the surface of 

 the pleura and upon the pericardium. These false membranes 

 exist upon one or both sides, as the case may be. Portions of 

 the lungs are found adherent to the sides and to the diaphragm, 

 but in many cases the bands of lymph are of a friable nature, 

 the adhesions very imperfect, and the opposing surfaces easily 

 separated, while there is, in old-standing cases, generally much 

 fluid in the cavity of the thorax, in which flakes of fibrin are 

 seen floating. The effused fluid is of a yellowish colour, con- 

 tains much albumen, and if exposed to the atmosphere will 

 often coagulate into a gelatinous clot. There is much variety 

 in the quantity of the fluid. In some cases the pleural cavity 

 and pericardium will contain several gallons, whilst in others 

 the quantity may only measure a few ounces. 



The pulmonary pleura, in addition to the bands of lymph, 

 which form the adhesions already alluded to, is invested by a 

 firm layer of lymph, which may be stripped off", leaving the 

 lung rough, mottled, and having papillse-like eminences upon its 

 surface. These bands of lymph, as well as the flakes found 

 floating in the serum, are composed of fibrin. When examined 



