cause purgation and bring it about more rapidly and powerfully than when the salt is taken by mouth. It was further shown by Aubert[38] that the purgative effect of various salts is not at all proportional to their endosmotic power nor to their concentration. Headland,[39] assuming without experiment that purgative salts act when introduced into the circulation, advanced the hypothesis that when they are given by mouth they are first absorbed into the blood and are later excreted by the intestine. In thus passing through the intestine he supposed that they stimulated the glands to secrete. Brieger,[40] using the method introduced by Colin and Moreau, obtained what he considered an increased secretion into the intestine. Isolating a loop of the intestine, he introduced into it a strong solution of MgSO_{4}. The loop became in a short time filled with a clear yellow alkaline fluid. This he believed was due partly to the water attracting power of the salt, and partly to the production of a real secretion. Vulpian[41] believed that the fluid was due to an inflammatory irritation. Hay[42] made experiments similar to those of Brieger, and found that the introduction into a loop of 10% Na_{2}SO_{4}, caused a considerable increase in the secretion, although no secretion was obtained by a 1-5% solution. Schmiedeberg[43] explained the presence of a greater quantity of fluid in the stools following the administration of the purgative by the supposition that the purgative salts on reaching the large intestine prevent the absorption of water. He states that these salts are themselves absorbed with difficulty and hence reach the lower part of the intestine unchanged. A similar hypothesis is advanced by Wallace and Cushny.[44] They stated that the absorption of fluid was inhibited especially by those salts which form insoluble compounds with calcium. These authors, however, did not take into account the possibility of the secretion of fluid into the intestine being increased by these salts. Hence their method of determining the difference in absorption of the various solutions is open to criticism, since it will be shown in this chapter that some if not all of these purgative salts cause a very definite increase in the intestinal fluid. The absorption of fluid may indeed be diminished by these salts, but it is difficult to say in the experiments of Wallace and Cushny how much of the fluid remaining in the loops is due to inhibited absorption, and how much has been actually secreted by the intestine. The experiments of Brieger[45] and Hay[46] in the production of increased secretion are quite unsatisfactory on account of the great concentration of the solutions used. Their results may well be ascribed to the local irritating effect of the strong solution, since they did not obtain an increased secretion with weaker solutions.