_Lesions._ In cases due to productive inflammation with sclerosis of the kidney, the firmness, pallor and bloodlessness of the organ is a marked feature. When incised it is found to be composed mainly of fibrous tissue, while the glomeruli and tubuli have to a large extent disappeared. If there has been simple lack of circulation the kidney becomes flaccid, pale and small in size. The secretory elements (glomeruli and uriniferous tubes) are first absorbed, leaving the fibrous network, which tends to shrink and form a hard resistent mass. In extreme cases there may be absolutely no glandular tissue left, and the dense shrunken mass represents only the hyperplasia of the original fibrous network. In the different successive stages of this process the glomeruli and tubules become flattened, the epithelial cells become granular, or contain colloid casts and refrangent elements like oil globules and finally they are represented by a small mass of fibrous material. Of all the atrophies caused by the pressure of tumors perhaps that caused by cysts is the most characteristic. There may be a single cyst or they may be multiple; they may range in size from a pea to the size of the two fists the total size exceeding that of the normal kidney. In all such cases the cysts project visibly from the surface of the organ. They vary according to their origin and nature. Congenital cysts are said to have resulted from distension by retained urine of the capsule of the glomerulus. The arterial tuft is atrophied and flattened against the wall. Serous cysts with clear contents are found in the old. Urinous cysts again form by distension of the tubules that are obstructed by cysts or minute calculi. Colloid cysts are found in certain forms of nephritis formed by the dilatation of the capsule of the glomerulus or of the uriniferous tubules. The liquid often contains leucin, tyrosin and cholesterine. In all such cases the walls of the cyst become thick, and the glandular parenchyma is compressed leading to progressive degeneration and atrophy. _Symptoms_ of atrophy of the kidney are necessarily those of suppression of urine, with, in certain cases, the passage of casts of the uriniferous tubes and of crystals of salts. There are, however, no absolutely pathognomonic symptoms. When the kidney can be reached through the flaccid walls of a comparatively empty abdomen, or through the rectum, its hard, shrunken condition may assist in diagnosis. _Treatment_ is not successful in advanced cases. _Prevention_ is to be sought by obviating or treating the conditions on which the atrophy depends. Nephritis must be treated on general principles. Calculi must be avoided by a liberal supply of water, by soiling, or by pasturage. Strongylus parasitism should be dealt with by destroying the parent worms in the bowels, and by securing pure drinking water free from their eggs and embryos. Cysts, and tumors are only amenable to surgical measures and not often open even to these.