Inability to pass urine may come from any one of three conditions--first, spasm of the neck of the bladder; second, paralysis of the body of the bladder; third, obstruction of the channel of outlet by a stone (calculus) (see Pl. XI) or other obstacle. In _spasm of the neck of the bladder_ the male animal may stand with the tail slightly raised and making rhythmical contractions of the muscle beneath the anus (accelerator urinÊ) (see Pl. IX, fig. 2), but without passing a drop of liquid. In the female the hind legs are extended, widely parted, and the back is arched as if to urinate, but the effort is vain. If the oiled hand is introduced into the rectum or vagina in the early stages of the affection, the bladder may be felt beneath partially filled, but not overdistended with liquid, and its neck or mouth firm and rigid. In the more advanced stages of the affection the organ is felt as a great, tense, elastic bag, extending forward into the abdomen. In this condition the overdistended muscular coat of the bladder has lost its power of contraction, so that true paralysis has set in, the muscle closing the mouth of the sac alone retaining its contractile power. In _paralysis of the body of the bladder_ attention is rarely drawn to the urinary disorder until the bladder has been distended to full repletion and is almost ready to give way by rupture and to allow the escape of the contained liquid into the abdomen. Overdistention is the most common cause of the paralysis, yet it may occur from inflammation of the muscular wall of the bladder, or even from injury to the terminal part of the spinal marrow. In this last condition, however, the tail is liable to be powerless, and the neck of the bladder may also be paralyzed, so that the urine dribbles away continuously. _Causes._--Among the causes of spasm of the neck of the bladder may be named the lodgment of small stones or gravel, the feeding on irritant diuretics (see "Bloody urine," p. 119, or "Nephritis," p. 123), the enforced retention of urine while at work or during a painful or difficult parturition. The irritation attendant on inflammation of the mucous membrane of the bladder may be a further cause of spasms of the neck, as may also be inflammation of the channel (urethra) back of the neck. Extensive applications of Spanish flies to the skin, the abuse of diuretics, and the occurrence of indigestion and spasms of the bowels are further causes. So long as spasmodic colic is unrelieved, retention of water from spasm of the neck of the bladder usually persists.