=Dilatation.= This is of not unfrequent occurrence, and is the result either of a paralysis of the muscular coat, or of some obstacle to the outflow of the urine. The dilatation may be uniform, or we may find diverticula, formed by a protrusion of the mucous membrane between the fasciculi of muscular fibres. Such partial distensions occur most frequently in the lateral portions, the posterior surface, or the neighborhood of the fundus, and as we should be led to expect from the manner of their formation, are generally destitute of a muscular tunic, or have but a few scattered fibres. Calculi are sometimes found in these pouches after death, the presence of which had escaped notice during life from their concealed position. =Hypertrophy= of the muscular coat of the bladder, will generally be found attending cases of obstruction to the escape of the urine, either from an enlarged prostate, stricture of the urethra, or from the presence of a calculus. The muscular coat in these cases is greatly thickened, the interlacing bundles of fibres appearing with great distinctness upon the inner surface. As a result of this condition, we usually find the bladder greatly contracted, its capacity in some cases being reduced to one or two ounces. Inflammation of the mucous coat, with dilatation of the ureters, will also generally attend, hypertrophy of the muscular walls. =Contraction= of the bladder is met with, as the result either of irritation of the mucous membrane, or hypertrophy of the muscular coat. =Inflammation= of the bladder is generally seen in its chronic form. The appearances in _acute cystitis_ are “strong vascular injection of the mucous lining, with brownish patches in the vicinity of the neck and fundus; more or less thickening of the membrane, with exudation of fibrin or pus on the surface, or foci of the latter in its substance. The mucous tissue may be ulcerated at several points, softened or affected by commencing gangrene. Abscesses may form in the substance of the parietes, and open either into the cavity of the bladder, or upon its external surface. Sometimes the mucous membrane is almost completely destroyed, a few shreds or filaments being the only traces remaining, while the muscular tunic is left as if cleanly dissected. This is probably the result of phagedenic ulceration.” The inflammation may spread from the mucous membrane to the muscular coat, but it very rarely reaches the peritoneal covering. In some cases it extends back along the ureters, and even to the kidneys. The morbid action is not often of idiopathic origin, it is more frequently due to the extension of an attack of gonorrhœa, to disease of the prostate, to traumatic causes, to protracted retention of urine, or to the irritation produced by medicines or stimulating drinks. It is sometimes owing to the constitutional poison of rheumatism or gout. It is met with oftener in men than women, and in adults than in children.