Loeb has recently made experiments on a jellyfish of the Pacific (Polyorchis) with results which are somewhat different from those described for voluntary muscles and Gonionemus. He found that the normal swimming movements of the uninjured animal could not occur in solutions which did not contain some proportion of magnesium, and the presence of magnesium in the sea-water seemed to be the stimulus for the apparently spontaneous movements of the animal. Calcium and potassium were found to oppose this action of magnesium. Further with the isolated center of Polyorchis, which will not beat in pure sugar solution or in sea-water, it was found that the addition of CaCl_{2}, SrCl_{2}, or BaCl_{2} to either solution caused contractions to appear. Magnesium chloride did not produce this effect. In pure NaCl solution also the isolated center will not beat, or beats only after a long time, while the addition of CaCl_{2} to the NaCl causes it to beat at once. Lingle[53] made experiments with the ventricle of the tortoise heart, which was able to beat for only a short time in pure NaCl solutions. When a small amount of CaCl_{2} is added, however, the heart may continue to beat for a long period. Lingle explained this by the assumption that NaCl is a poison and that calcium acts in an antitoxic way, a suggestion already offered by Loeb. Loeb’s experiments on the inhibition of muscular twitchings in voluntary muscles by calcium and magnesium, as well as the similar results he obtained with the isolated center of Gonionemus, led me to test the action of these two substances on the rhythmical movements of the mammalian intestine. It was found that not only the normal movements of the intestine, but also those produced by the saline purgatives such as sodium citrate, sulphate, tartrate, etc., could be very definitely inhibited by the administration of calcium or magnesium chloride. This was the case when these latter substances were given in any way either intravenously, subcutaneously, or applied directly to the serous surfaces of the intestine. The following experiments will illustrate this inhibitory action. A rabbit was anaesthetized by a subcutaneous injection of 4-5 c.c. 1% morphine solution. The intestines were then carefully exposed and protected in every way from loss of heat and moisture. The method suggested by van Braam-Houckgeest[54] of opening the abdomen under the surface of sodium chloride solution is perhaps the most perfect. A small quantity of m/6 sodium citrate solution (for a rabbit weighing 1,200 g. 2-3 c.c. is sufficient) was injected into a vein of the ear. The intestines almost immediately began to move actively. There was then injected 3-4 c.c. m/6 CaCl_{2} solution. The intestines within 2 or 3 minutes came entirely to rest and remained perfectly quiet. A second injection of a somewhat greater quantity of sodium citrate caused them to again become active.