It is generally believed that the normal peristaltic wave passes only from above downward, and never in the reverse direction. This has been shown in many ways. Mall[4] removed a certain length of the small intestine and reversed it so that the end which had originally been nearer the stomach was now in the position formerly occupied by the end nearer the rectum. The food would not pass down this part of the intestine, but accumulated above it. In other words, the peristalsis continued as it was before the loop was removed, the wave passing in the reversed loop from below upward. A further illustration of the same thing is seen in the fact that in an isolated loop an object inserted in the gastric end of the loop will rapidly be passed to the other end, while it is impossible to force the object into the rectal end because of the peristaltic waves which constantly expel it. Grützner[5] observed that the intestinal contents sometimes move backward and forward in the intestine, and that an easily recognizable substance, _e.g._, food introduced into the rectum _in enemata_, was sometimes to be found afterwards in the stomach. It seems further from Cannon’s[6] study of the cat’s intestine by means of the Röntgen rays that antiperistalsis certainly takes place in the colon of this animal. In the transverse and ascending colon antiperistaltic waves occur at the rate of 5-6 per minute. No antiperistalsis was observed in the small intestine. _Factors which normally cause or influence the intestinal movements._ Although there has been some divergence of opinion on the subject, it is now generally held that anaemia of the intestine causes a cessation of all movements. This has been shown by van Braam-Houckgeest,[7] Mall,[8] and others. Clamping of the aorta, opening of the heart, etc., cause all movements to cease. Hyperaemia of the intestine on the other hand causes active movements to arise. Any conditions which cause a venous engorgement of the intestine bring about intestinal movements. Bokai[9] found that CO_{2}, is a direct stimulant to the intestine, and that the movements may be stopped by the application of oxygen. Krause and Heidenhain first noticed that when an animal’s breathing is stopped the peristaltic movements of the intestine greatly increase, but cease when the breathing is recommenced.