If it is decided that the drug acts on some part of the intestine to cause the peristalsis, two methods may be used to determine what part it acts upon: 1st Method.—After performing tracheotomy, opening abdomen and destroying abdominal ganglia, place the animal in a tin vat containing warm physiological solution. The first thing is to find out:— (1) Whether the cathartic acts reflexly by the irritation of the mucous membrane being transmitted to Auerbach’s plexus, and from there to the muscles, or (2) Whether it acts upon some structure in the intestinal wall after being absorbed. _Demonstration._—If it acts reflexly, it will act quicker when injected into intestinal canal than when injected into mesenteric artery. If it does not act reflexly, it will act quicker when injected into the artery. Next determine where in the intestinal wall the cathartic acts. The points are: 1st. Stimulation of the muscle. 2d. Depression of the inhibitory motor ganglia. 3d. Stimulation of Auerbach’s ganglia, and, 4th. Stimulation of the motor fibres. _Demonstration._—If the drug in large dose causes tetanic spasm of the intestinal muscles, which is not affected by electrical stimulation of the inhibitory motor nerves, this shows that the drug acts directly on the muscles. In this way it can be shown how physostigmine acts. If the drug in large dose increases peristalsis, and electrical stimulation of inhibitory motor nerves has no effect upon it, this shows that the drug paralyzes the inhibitory motor nerves. It can be shown that morphine acts in this way. In fifteen or twenty minutes after giving a dog a grain of morphine hypodermatically, it usually has one movement of the bowels. A small dose of morphine constipates, because it stimulates the inhibitory motor nerves. If the drug increases peristalsis and stimulation of the inhibitory motor nerves lessens the peristalsis, this shows that the drug either stimulates Auerbach’s ganglia, or the ends of the motor nerves. By the method above described Jacobi has made some very elaborate experiments with morphine, atropine, muscarine, and physostigmine. 2d Method.—A piece of excised living intestine is placed in a suitable apparatus to keep it moist and warm, and artificial circulation is established by a canula in the artery, connected with two flasks, as seen in the drawing copied from Brunton (Fig. 8), in one of which is pure blood and in the other the poisoned blood, arranged so that either can be turned on at will. The peristalsis is recorded by the lever, shown in the drawing. In this way Ludwig and Salvioli studied the action of a number of drugs. [Illustration: From Brunton.] ACTIONS OF CATHARTICS IN DISEASE.