390 DISEASES OF THE KIDNEYS 



by vehicles, falling, etc., which may result in direct injuries 

 to the kidneys and eventually in acute inflammation. Sub- 

 jection to extreme cold has been considered one of the etio- 

 logical factors: It probably reduces the general resistance 

 of the renal tissue so that infectious substances have a greater 

 effect upon it. This has been observed, especially in puppies 

 and kittens that have been kept in damp, cold kennels. The 

 same thing is found in hunting dogs after being forced to 

 wade or swim through cold water. 



Pathology.— This is usually divided into three classes as 

 follows: 



(a) Parenchymatous nephritis, in which the primary inflam- 

 matory changes are most pronounced in the parenchyma of 

 the kidney. This is characterized by only slight swelling, 

 the capsule more easily removable, and on cut section a 

 grayish or dull color is noted. Sometimes there will be 

 observed grayish-red or yellowish-brown spots. The medul- 

 lary substance is hyperemic, often dark red in color and the 

 Malpighian bodies are quite prominent, while the balance 

 of the organ is either normal or of a soft consistency. 



Microscopically the veins and capillaries are enlarged, 

 congested, granular and fibrous deposits between the urinif- 

 erous tubules, and epithelial casts, cells, fatty degeneration 

 with swelling and opacity. 



(b) Hemorrhagic parenchymatous nephritis, which is char- 

 acterized by a large number of red points giving the external 

 appearance of the organ a dark red color, dull gray on 

 section, blotches of red and in the medullary portion a 

 deep red. 



Microscopically the veins and capillaries are found engorged 

 with blood, hemorrhages appearing in the adjacent tissues. 



(c) Diffuse Acute Nephritis.— -Very noticeable is the in- 

 crease in size and weight of the organ, sometimes two or 

 three times larger than normal. The tissues are soft and 

 friable. The capsule is easily removed, and the external 

 surface a bright red color with some yellowish or gray patches. 



Microscopically there will be found enlargement of all 

 vessels with extensive extravasation of blood into the tissues, 

 leukocyte casts in the dilated urinary ducts, and extensive 



