Minute Lesions.--Nearly all the component parts of the kidneys undergo morbid changes. In the tubes the epithelial cells undergo marked changes, especially in the cortex. The epithelial cells are swollen, finely or coarsely granular, or fatty or completely disintegrated, or the seat of hyaline degeneration. They may be detached from the walls of the tubes, or sometimes they are in place, but flattened. The tubes may contain cast-matter, blood, pus-cells, small polygonal cells. The calibre of the tubes is often changed. The tubes may be dilated either in the form of cylindrical or sacculated dilatations; the latter often form cysts of considerable size. Such dilatations regularly affect groups of tubes, as if they were due to obstruction of the large tubes in the pyramids. In other cases the tubes are denuded of epithelium, become smaller, fall together, and look like connective tissue. The membranous wall of the tubules may be thickened or it may undergo waxy degeneration. The Malpighian bodies are changed. Their capsules may be thickened, contracted, or dilated. The flat cells which line the capsules are increased in size, sometimes in number. The capillary tuft may be dilated or its walls may be thickened; it may be completely obliterated and changed into a ball of fibrous tissue, or it may be the seat of waxy infiltration. Often the Malpighian bodies are much closer together than they are in a normal kidney. {87} In the stroma, especially in the cortex, there is a new growth of connective tissue. This new connective tissue is in patches of varying size, surrounds Malpighian bodies and blood-vessels, and may be continuous with the capsule of the kidneys. The arteries are frequently changed. There is a general thickening of all their coats, usually a simple sclerotic thickening. All these changes, when they have once begun in the kidneys, have a natural tendency to go on and become more and more marked. There is much difference in different kidneys in the predominance of one or more of these changes over others. In one kidney the changes in the tubes will be most marked, in another those in the Malpighian bodies, in another those in the stroma. But there seems no good reason for believing that these changes are developed successively--that there is first a lesion of the stroma, then a lesion of the tubes, or first a lesion of the tubes, and then of the stroma. The earliest examples of chronic diffuse nephritis, obtained from persons dying accidentally of other diseases, show that the lesions are diffuse at the very outset.