It is determined by irritation caused by calculus, urethritis, ulcer, wounds, etc., which tend to the formation of a cicatrix encircling and narrowing the canal. One efficient cause is the injection of strong astringent or slight caustic solutions in the early stages of urethritis. _Treatment_ is by dilation, by bougies pointed and gradually thickening, or simply by an elastic staff which at first passes with some force and is replaced by a larger one as the urethra stretches under daily use. =Catheterization.= In connection with diseases of the bladder and urethra the passing of the catheter is a most important operation which requires considerable skill on the part of the operator. A short statement of the method to be adopted for each of the domestic animals will therefore be in place. =Catheterization in the male Soliped.= The catheter, a hollow, gum elastic tube, must be proportioned to the size of the animal, but for the average adult horse about 3½ feet in length and ⅓ inch in thickness. To give it the requisite solidity and resistance it is usually furnished with a stilet of whalebone or cane. The operation is performed with the animal standing, in quiet animals without any restraint, but in the more sensitive or restive, with one fore foot held up; or with both hind feet in hobbles furnished with ropes passing between the fore limbs and tied over the neck in front of the withers; or finally with a twitch on the nose. The rectum is emptied, and with the oiled or soapy hand the penis is found and slowly withdrawn from the sheath by steady traction. This is usually easy, though in certain cases, with a short penis and specially strong retractors, it will seriously tax the operator’s skill and address. In a specially obstinate case a hypodermic injection of morphine may be resorted to. If the horse is down, as in paraplegia or hæmoglobinæmia, he may lie on his right side while the operator stoops over him from the loins; or his feet may be drawn together by hobbles, and the subject turned on his back, the operator placing himself as before on the left side. The catheter must have been previously cleansed and disinfected outside and in. A mercuric chloride solution 1:2000, or boric acid 1:50 or permanganate of potash 1:50 may be employed. Then it must be smeared, preferably with vaseline but, in case of necessity, with sweet oil, glycerine, borated lard, or even castile soap. The penis being withdrawn from the sheath, the catheter containing its stilet is introduced into the urethra and pushed on slowly and carefully until its point can be felt over the ischiatic arch. The stilet is now drawn out a few inches and the point of the catheter is bent forward over the ischium by the finger. The stilet is further drawn out and the catheter can easily be pressed on into the bladder. If any difficulty is experienced it may be guided by the hand introduced into the rectum.