have been repeatedly demonstrated. In pyelonephritis the Bacillus coli communis is probably the usual active etiologic agent. Streptococci occur in the nephritis of septic conditions and in primary infectious nephritis of cryptogenic origin. Bacteria are occasionally found in the uriniferous tubules without gross lesions of the kidney, and are probably excreted with the

urine.

Streptococci occur in the urine in the nephritis of septic conditions, and in primary infectious nephritis of cryptogenic origin. Various other bacteria may be met with in the urine (see Bacteriuria).

Animal parasites are occasionally observed, such as echinococcus-cysts, filariæ, the eggs of Distoma hematobium, amœbæ, and infusoria. Round worms and the oxyuris sometimes migrate into the bladder or enter through fistulæ.

The echinococcus-cyst occurs in the form of hydatids, which may perforate into the pelvis of the kidney and discharge with the urine, or become inspissated and calcify. The Cysticercus cellulosa and Pentastomum denticulatum are extremely rare. The Filaria sanguinis hominis occurs in the lymphatic spaces and in the blood-vessels of the kidney in cases of filariasis with chyluria. The kidneys in these cases show a waxy appearance on section, especially toward the apices of the pyramids, and the surface of the kidney may be abnormally lobulated. Microscopically the lymphatic spaces about the uriniferous tubules are greatly distended.

The Distoma hematobium occasionally produces pyelitis and pyelonephritis, with enlargement of the pelvis of the kidney.

THE PELVIS OF THE KIDNEY AND URETER.

CONGENITAL AND ACQUIRED MALFORMATIONS.

Occasionally the pelvis or ureters, or both, may be absent or imperfectly developed. Complete obliteration of the ureter may be observed. More frequently there are two pelves or ureters, and when this is the case the malformation is, as a rule, bilateral.

Obstructions of the ureter may be due to twists, to congenital atresia, or to other diseases of the ureter, particularly at its entrance into the bladder. It may be brought about by the lodgement of renal calculi, by tumors of the ureter, or by pressure upon it from without. The outflow of the urine may be obstructed by diseases of the bladder, and particularly by stricture of the

ureter.

Dilatation of the ureter results from the conditions just named, and may reach considerable dimensions (Fig. 287). When

the obstruction is continued the dilatation may affect the pelvis of the kidney as well, and eventually the latter may be enor

mously enlarged. The pyramids become flattened, and the renal substance may undergo progressive atrophy, so that the kidney is converted into a sac-like formation filled with clear liquid, partly urine secreted in the earlier stages and partly transudate formed after the compression has stopped the renal function. To this condition the term hydronephrosis is applied.

CALCULUS.

Calculi are of frequent occurrence in the pelvis of the kidney, and are formed by the precipitation of various normal or abnormal constituents of the urine. There may be merely small gritty particles lying in the calices or in the pelvis, to which the term renal sand, or gravel, is given; or there may be large stones, almost filling the pelvis and calices, and forming more or less accurate moulds of these. The most frequent forms are those composed of uric acid and oxalate of lime, but phosphate and carbonate of calcium and triple phosphate calculi are occasionally found. Stones composed of cystin and xanthin are rare. Uric-acid calculi are composed of the acid itself, or of urates, and present themselves as yellowish, brownish, or red, smooth or somewhat irregular formations. Those composed of oxalate of lime are irregular in shape and of brownish or red color.

The results of renal calculi may be trivial or serious. Small particles of renal sand are frequently passed without serious disturbance. Large calculi tend to set up inflammation of the pelvis of the kidney, and may obstruct the outflow of the urine, causing hydronephrosis (Fig. 288). In some cases cancer seems dependent upon the continued irritation of a retained calculus.

INFLAMMATION.

Inflammation of the pelvis, or pyelitis, may result from the irritation of poisons ingested, such as cantharides, turpentine, and the like, or it may occur in the course of infectious diseases of various kinds. More frequently it results from the irritation of a calculus, or from ascending inflammation consequent upon cystitis

and ureteritis. The mucous membrane becomes reddened and swollen, and not rarely is marked with hemorrhagic ecchymoses. The surface is covered with more or less desquamated epithelium and pus-cells. The inflammation may extend to the substance of the kidney (pyelonephritis). Considerable purulent exudate may take place, particularly when there is a calculus partially obstructing the ureter. When there is complete obstruction the pelvis may become dilated with pus, and the calices or the entire kidney may be converted into a large pus-sac (pyonephrosis). Deposits of triple phosphate may occur in pyelitis, and may occasion incrustations upon the mucous surface.

Inflammation of the ureter, or ureteritis, may occur under the same conditions as pyelitis. The mucous membrane of the ureter becomes swollen and reddened, as in catarrhal inflammations elsewhere, and

there may be erosions or superficial ulcerations. The other coats are thickened by inflammatory infiltration and, in chronic cases, by fibrous-tissue overgrowth.

FIG. 289.--Tuberculous pyelonephritis (modified from Bollinger).

INFECTIOUS DISEASES.

Tuberculosis of the pelvis of the kidney may occur as a miliary tuberculosis, or in the form of caseous nodules or masses. The latter may be primary and hematogenous in origin, or may

result from ascending infection (Fig. 289). In such instances the mucosa becomes more or less extensively infiltrated, and later caseous and ulcerated. The process extends to the calices, and subsequently to the pyramids and other parts of the substance of the kidneys. The pelvis may contain considerable quantities of caseous or puriform matter, and the kidney-substance may be extensively involved. The urine contains pus-corpuscles and often tubercle bacilli in great numbers. Tuberculosis of the ureters leads to nodular or diffuse thickening, and commonly to more or less obstruction (Fig. 290).

TUMORS.

Primary cancer is extremely rare.

Secondary cancer may affect the pelvis in association with the kidney, or the ureters in association with the bladder. Small cystic formations are not uncommonly seen in the mucous membranes of the ureters, and may be due to inflammatory obstruction of the crypts, to proliferation and softening of the lymphoid follicles, or to parasitic invasion (psorospermia).

PARASITES.

Round worms have occasionally been found in the ureters. The eggs of Distomum hæmatobium are frequently deposited in the mucous membrane, and occasion inflammation and papillom

atous excrescences.

THE URINARY BLADDER.

MALFORMATIONS.

Congenital malformations of the bladder are comparatively common. Among the more important is exstrophy. The anterior wall of the abdomen and of the bladder being wanting, the mucous membrane, with the openings of the ureters, is exposed to view. Not uncommonly this condition is associated with epispadias, or division of the clitoris. Sometimes the small intestine discharges through the exstrophic bladder, the large intestine being contracted or completely absent.

Occasionally the urachus remains patulous in consequence of atresia of the neck of the bladder or urethra, and the urine is discharged from the umbilical end. In other cases the urachus is closed at either end and the intervening portion is dilated, with the formation of a cyst. Again, there may be only partial obliteration of the urachus, the remaining portion in connection with the bladder being patulous and greatly dilated, forming a congenital adventitious sac. In one case under my observation this constituted a cavity of considerable size, and when filled distended the abdomen as far as the umbilicus. Congenital diverticula may occur in the anterior wall, and less commonly at the sides of the bladder. Complete absence of the bladder, division into lateral portions by a septum (vesica bipartitis), and other congenital defects are rare.

Acquired Malformations.-Dilatation of the bladder may result from congenital or acquired stenosis of its neck, or of the urethra; or from paralysis of its walls, in consequence of disease of the spinal cord or nerves. The organ may be greatly increased in size, often reaching the umbilicus. When the dilatation is acute the walls are greatly thinned, but when it has been gradually developed compensatory hypertrophy of the muscularis and of the submucous fibrous tissues leads to thickening of the walls. In these cases the mucous surface presents a ribbed appearance, fibrous-tissue bands standing out prominently and the mucosa being pouched between the bands. Diverticula of considerable size may form in this way, and the walls of the bladder sometimes present a considerable number of pouches.

CHANGES OF POSITION.

The position of the bladder, or of portions of it, is sometimes abnormal. Thus it may enter into a hernia, or a part of the wall of the bladder may prolapse with the wall of the vagina, forming vaginal cystocele. The latter is due to the traction of the prolapsing uterus, or to repeated overdistention of the bladder, with