38 DISEASES OF THE KIDNEY. 



The color of the renal substance becomes of a dirty brown or gray, 

 owing to compression of its vessels by the interstitial exudation, which 

 already, here and there, contains pus. 



The discoloration usually begins at detached points, of the size of a 

 hemp-seed. As it increases, these spots soften, until they finally break 

 down into a purulent liquid. In this way small abscesses form, by the 

 melting down of the renal substance, under the pressure of the con- 

 stantly-accumulating pus-cells. In the cortical substance, the form of 

 the abscess is more rounded ; in the pyramidal, more elongated. The 

 abscesses enlarge and coalesce, finally forming a great sac of matter, 

 which may occupy one-half or even two-thirds of the kidney. Such 

 an abscess may become incapsulated, and long remain embedded in 

 condensed cellular tissue. In other cases, the deposits discharge in 

 various directions, as into the pelvis of the kidney, the cavity of the 

 abdomen, externally through long fistulous tracks, into neighboring 

 parts of the intestine, which have become adherent to the wall of the 

 abscess, or even, through the diaphragm, into an adherent portion of 

 the lung. When the disease runs a more chronic course, it sometimes 

 terminates differently. In such cases the interstitial substance of the 

 kidney undergoes proliferation, while the peculiar tissues of the organ 

 perish. At the close of such an attack of chronic interstitial nephritis, 

 the kidney is irregular, and nodulated in shape. The elevations are 

 more marked than those of the third stage of Blight's disease, and 

 the albuginea is firmly adherent in the sulci between them. Upon 

 cutting into one of these depressed spots, instead of renal-tissue proper, 

 we find nothing except the indurated substance of a cicatrice. 



The metastatic nephritis, which accompanies disease of the heart, 

 shows no tendency to suppuration. In recent cases, distinctly circum- 

 scribed, dark-red cuneiform spots are found in the kidney. The base 

 of the wedge lies toward the periphery of the organ, the apex toward 

 its hilus. Microscopic examination shows an intense engorgement of 

 the vessels with dark masses of blood, blood being also effused into 

 aud between the tubules. Haemorrhagic infarction of the kidney, when 

 of longer standing, undergoes metamorphosis similar to that already 

 described as occurring in haemorrhagic infarction of the spleen. A dis- 

 coloration commences in the middle of the point of infarction, which, 

 having undergone a complete fatty metamorphosis, and all the fat 

 having been absorbed, cicatrizes, leaving a depressed scar. The me- 

 tastatic deposits which form in the kidney in infectious disease, and in 

 consequence of the absorption of putrid matter into the blood, are 

 generally much smaller, and far more numerous, than the infarctions 

 which occur in disease of the heart. Moreover, their tendency to break 

 down is very great, so that, upon examination, it is not usual to find 



