INTERSTITIAL NEPHRITIS REN AL ABSCESS. 37 



mainly in the scanty connective tissue which binds the tubules together. 

 The most common causes of true nephritis are as follows : 



1. Wounds and contusions. The kidney is seldom subjected to 

 external violence, owing to its sheltered position. It is far more liable 

 to injury from the presence of stones within the pelvis of the kidney. 



2. Collections of decomposed ammoniacal urine in the pelvis of the 

 kidney, the result of urethral stricture, enlargement of the prostate, 

 palsy of the bladder from injury of the spine, and so forth. Here the 

 irritation to which the kidney is subject is of a chemical instead of a 

 mechanical nature. 



3. Propagation of inflammation from the urinary passages to the 

 kidney. It is easy to comprehend that an inflammation of the pelvis 

 of the kidney, a pyelitis, might readily extend into the parenchyma of 

 the organ, and cause nephritis ; but the fact that nephritis is sometimes 

 associated with gonorrhoea, but is not a result of extension of the latter 

 disease by contiguity, and where there is no accumulation of urine in 

 the pelvis'.pf the kidney, is altogether enigmatical. 



4. Propagation of the inflammation from the connective tissue of 

 surrounding parts, the peritonaeum and other organs. This is the 

 rarest of all the modes of origin. 



5. Embolism of small arteries of the kidney, and the introduction 

 of septic or miasmatic material into the blood. This is the source of 

 the so-called metastatic nephritis, observed in endocarditis, valvular 

 disease of the heart, and in the various disorders classed under the 

 general title of pyaemia, as well as in the infectious diseases. 



There is usually no doubt as to the embolic origin of the cuneiform 

 deposits, which, in the disease of the heart above alluded to, occur 

 almost as frequently in the kidney as in the spleen ; but it is sometimes 

 extremely difficult to trace the origin of the small metastatic deposits 

 which form in the kidney during the later stages of septicaemia, puer- 

 peral fever, typhus, etc., to the action of embolism. It is questionable 

 whether interstitial nephritis ever arises from the effect of cold, or from 

 that of acrid diuretics. 



ANATOMICAL APPEARANCES. In traumatic nephritis, or in ne- 

 phritis arising from an extension of inflammation from the pelvis of 

 the kidney, or from other organs, the kidney at first is enlarged, and 

 is of a deep-red hue, which is either diffused over its whole substance, 

 or else is confined to single spots in the cortical or medullary portion. 

 Its consistence is much less firm. The albuginea is injected, thickened 

 by infiltration, and easily detached. Upon section, the structure is 

 indistinct, and the boundary between the cortical and pyramidal sub- 

 stance is effaced. A bloody, thick liquid can be expressed from the 

 surface of the cut. At a more advanced stage the redness subsides. 



