STRUCTURAL CHANGES DUE TO DAMAGE. 



317 



surfaces. In the exudate, besides the usual constituents, there are 

 desquamated epithelial cells and a variable amount of mucus. 

 Mucus, it will be remembered, is a substance normally secreted upon 

 the mucous membranes, where it serves to protect the underlying 

 cells. When those membranes are irritated the supply of mucus is 

 increased. In catarrhal inflammations it may be so abundant as to 



FIG. 280! 



5iv 



1 V^SQA 'ij^.^'^ 



Serous leptomeningitis : a, cedematons fibrous tissue of the pia mater, the fibrous elements of 

 the tissue being separated by the serous exudate ; 6, group of leucocytes, probably held 

 together in part by fibrin; c, granuliir fibrin and detritus; b and c, and other similar 

 masses, lie in the serum, which occupies the whole field between the visible elements. 



predominate over the elements of the exudate, so that the fluid 

 appearing on the surface of the membrane has a viscid character. 

 In other cases the mixed secretion and exudate may be muco-serous 

 or muco-purulent (Fig. 281). 



In catarrhal or broncho-pneumonia the exudate appearing in the 

 alveoli of the lung is of a serous character, with an admixture of 

 desquamated cells from the alveolar walls and a variable number of 

 leucocytes. These sometimes give the exudate an almost purulent 

 appearance. 



6. Croupous inflammation is an inflammation of a surface, char- 



