628 THE URINARY ORGANS. 



Between these types of lesion, largely based, as will be seen, upon the 

 relative involvement of the structural units of the kidney, are niaiiy in- 

 termediate forms which the scope of this book does not permit us to 

 consider. 



Kidneys which are the seat of acute diffuse nephritis sometimes ap- 

 pear almost normal on gross inspection. But in more typical forms they 



FIG. 389. ACCTE DIFFUSE NEPHRITIS. 



A vertical section of the cortex, showing the wedge-shaped growth of connective tissue with atrophy of 

 the glomeruli and tubules in the region especially involved, which is the territory of one of the interlobular 

 arteries. This is acute nephritis of the productive type. 



are slightly or considerably enlarged, the capsule is free, the cortex is 

 thickened, and either reddened or pale or mottled red and gray. When 

 the interstitial tissue is cedematous the cortex may appear translucent. 

 The glomeruli may be red or pale and conspicuous or normal in appear- 

 ance. The pyramids may seem unusually red by contrast with the 

 thickened pale cortex. In hsemorrhagic forms of acute nephritis in 

 which blood may collect in the glomeruli in the interstitial tissue and in 

 the tubules, the cortex may be mottled with red. 



In many forms of acute diffuse nephritis, particularly if the inter- 

 stitial tissue be not considerably involved, resolution may take place. 



The Excitants of Acute Diffuse Nephritis. In many cases of acute dif- 

 fuse nephritis, the process seems to be due to toxic substances which are 

 formed under the influence of micro -organisms in other parts of the body 

 and presumably excreted by the kidney with whose cells they come into 

 intimate contact or in whose metabolism they may share. Acute nephritis 



