ACUTE PARENCEYMATOUS NEPHRITIS. 409 



degeneration ; or of a uniform gray color in advanced stages, 

 when the leukocytic infiltration has been excessive contrast- 

 ing strongly with the pyramidal portion, which is generally 

 deeply congested. 



Microscopically, also, the appearances presented in acute 

 parenchymatous nephritis differ greatly both in the extent 

 and character of the lesion. In some instances the changes 

 are almost entirely confined to the tubular epithelium ; 

 resembling rather an acute degeneration than an inflammation. 

 At other times there is a diffuse inflammatory infiltration, in 

 addition to more or less marked changes in the tubular epi- 

 thelium (Fig. 191) ; in still other cases, to which the term 

 glomerulo-nephritis has been applied, the inflammatory changes 

 begin in and are most marked around the glomeruli, though 

 sooner or later becoming more general. 



Just what the essential differences are, in the character of 

 the exciting cause, which are factors in producing the varied 

 lesions noted above, is not kno\vn ; though it might be argued 

 that, when the poisonous substance or irritant is being elimi- 

 nated by the epithelial cells of the secreting tubules, the 

 changes may be most marked there ; but if of such a character 

 as to be more readily eliminated with the watery constituents 

 of the blood by w r ay of the glomeruli, the primary inflamma- 

 tory changes may be excited at that point. 



The changes in the uriniferous tubules, most marked in the 

 convoluted portions in the cortex, consist of a granular and 

 fatty degeneration of the epithelial cells, some of which 

 become desquamated and distend the tubules ; at the same time 

 the epithelial cells in places may show proliferative changes. 

 The epithelium of the glomeruli may undergo similar degen- 

 erative and proliferative changes, and the whole tuft become 

 enlarged from engorgement of its bloodvessels. Migrated 

 leukocytes, and small masses of extravasated red blood -cor- 

 puscles, are often seen in and around the tubules and glomeruli. 

 To this class of cases, in which the parenchymatous changes 

 are the most marked feature, the term catarrhal or desqua- 

 mative nephritis has been applied. 



As has been noted, in some cases, especially those occurring 

 in the course of scarlet fever, the inflammatory changes begin 

 in the Malpighian bodies glomerulo-nephritis. The glomeruli 



