Various subdivisions of Bright's disease have been made both from the clinical and the pathological points of view. The most generally accepted division is into parenchymatous and interstitial nephritis, to which some add the amyloid kidney.

Inflammations of the kidney have similar characters to those of other parts. In Acute inflammations the vessels are chiefly engaged at the outset; there is hyperemia with exudation of serous fluid, leucocytes, and red corpuscles. These find their way into the tubules and interstitial tissue, and appear in the urine as albumen, leucocytes, and red corpuscles. Death seldom occurs at the outset of the attack, and the appearances found post mortem are referable rather to secondary changes, chiefly in the secreting structures. Hence acute nephritis is included mainly under parenchymatous nephritis.

Chronic inflammation in the kidneys, as elsewhere, is chiefly characterized by new-formation of connective tissue, and hence is included, for the most part, under interstitial inflammation.

It is to be understood, however, that as parenchymatous and interstitial changes are by no means mutually exclusive, and indeed frequently co-exist, so also the phenomena of acute and chronic inflammation are not limited to the one or the other form.

(A) Parenchymatous Nephritis (Tubular Nephritis)

Parenchymatous nephritis is, at the outset, usually acute, and it nearly corresponds with the clinical group, acute nephritis, in which the urine is scanty, highly albuminous and frequently bloody, and in which general o?dema is a characteristic feature. But acute nephritis frequently subsides into a sub-acute or chronic stage, and in these, while the parenchymatous changes are still prominent, there are superadded some of the lesions of interstitial nephritis.

In parenchymatous nephritis the secreting structures are spocially engaged, namely, the glomeruli and tubules, but the degree in which these are respectively affected varies somewhat.

In ordinary cases the Uriniferous tubules show very marked changes. These consist in the first place in cloudy swelling of the epithelium with a tendency for the cells to become loosened and shed. The enlargement of the epithelium, occurring mainly in the cortical tubules, causes the latter, under the microscope, to present a strikingly prominent varicose appearance. There are also parts in which the desquamated epithelium distends or chokes the tubules. Fatcy degeneration soon affects the epithelium, and it is often present in a very high degree. It does not affect the epithelium uniformly, but at intervals there is a coil of tubules with the epithelium highly fatty (see Fig. 422). The fatty epithelium may be dislodged and packed into further parts of the tube, as into the loops of Henle, so that one often sees a straight tubule occupied by fatty epithelium.

Blood is not uncommonly present in the tubules. As the blood escapes from the vessels of the glomeruli it is found in the con-voluted tubules. The blood in these tubules is often detectable by the naked eye after removal of the capsule by the presence of small red or brown spots on the surface of the kidney. By the aid of a lens these can sometimes be made out as convolutions filled with red matter. Under the microscope fresh blood-corpuscles may be found distending the tubule and flattening its epithelium as in Fig. 423, or the blood may be altered so as to form a brown debris. The altered blood, although chiefly in the convoluted tubules, may extend into the straight ones.

Tube-casts are present in the form usually of translucent hyaline cylinders in the calibre of the tube. They are contained both in the convoluted and straight tubules, and they may be abundant in the pyramids.

As the case becomes more chronic the tubules are liable to considerable distortion, chiefly from the occurrence of interstitial changes. There may be irregular dilatations and contractions of the tubules, but the fatty condition of the epithelium remains prominent.

The Glomeruli show various changes. In some cases of scarlet fever there is in the glomerulus and around it a great exudation of leucocytes, which may fill the capsule and crush the tuft so as to conceal it (Fig. 427). The leucocytes also over-run the neighbouring interstitial tissue to a considerable extent, and the conditions may approach to those in septic nephritis. There may indeed be a septic element in many cases of scarlatinal nephritis (see below).

Uriniferous tubules with fatty epithelium, some of it shed into the calibre, x 300.

Fig. 422. - Uriniferous tubules with fatty epithelium, some of it shed into the calibre, x 300.

A coil of tubules distended with blood corpuscles.

Fig. 423. - A coil of tubules distended with blood-corpuscles. The epithelium is flattened agaijist the wall, x 300.

The Glomeruli commonly present, in various degrees, changes in their epithelium similar to those in the tubules. There may be merely an enlargement of the epithelium, so that instead of a thin layer which is usually invisible, it may form a distinct row of cells inside the capsule (Fig. 424). In many cases the epithelium multiplies and accumulates inside the capsule (Fig. 425), and the cells sometimes take on a stratified arrangement which has suggested to some authors that connective tissue is formed inside the glomerulus. The epithelium covering the tuft of vessels is affected as well as that lining the capsule.

Glouierulo nephrit s in scarlet fever.

Fig. 424. - Glouierulo-nephrit s in scarlet fever. The epithelium lining the capsule is unduly largo and abundant, x 860.

Glomerulonephritis in scarlet fever.

Fig. 425. - Glomerulonephritis in scarlet fever. The epithelium lining the capsule is greatly increased so as to crush the tuft, x 350.