Mode of Action of the Saline Cathartics. Since the discovery of sodium sulphate by Glauber in the middle of the seventeenth century, and the preparation of the double tartrate of sodium and potassium at Rochelle some fifteen years later, the saline cathartics have been in constant use among physicians. Attempts have been made also from the first to explain in some way their mode of action; but it was not until the discovery of the osmotic property of salts that any explanation which seemed satisfactory was made. Poiseuille[76] and Liebig[77] both advanced the theory that the purgative action of salts was due to their power of attracting water into the lumen of the intestine, i.e., to their power of endosmosis. This seemed at first sight to be very satisfactory and to account well for the increased amount of fluid in the faeces following the administration of a saline cathartic. The theory did not, however, take into consideration other substances whose osmotic power is as great as that of the purgative salts, but which have no purgative action whatever. It was later, however, supported by Rabuteau[78] in an experiment in which he claimed to have found that the intravenous injection of a large quantity of sodium sulphate produced constipation, while the same salt given by mouth causes purgation. This he ascribed to the flow of fluid towards the salt in each case due to its osmotic pressure. This experiment lacks confirmation, and indeed it has been shown above that sodium sulphate and other saline cathartics produce increased peristalsis and in some cases increase of fluid in the intestine when introduced intravenously or applied on the serous surfaces of the intestine. And these evidences of a purgative action appear much more rapidly and with smaller doses than when the salt is placed in the lumen of the intestine. Claude Bernard[79] states in his criticism of this theory that the intravenous injection of sodium sulphate causes purgation, and further draws attention to the fact that on this theory of the endosmotic action of cathartics, sugar, which has a high osmotic power, should be among the more powerful purgatives. It was further shown by other investigators that of several purgative salts, the most powerful was not the one with the highest osmotic power. Headland,[80] believing that all medicines must first pass into the circulation before they act, claimed that the saline purgatives are absorbed from the intestine and are again excreted lower down in the intestine, and in being excreted they stimulate the glands to secrete. A little later than this it was shown by Moreau[81] and others that solutions of purgative salts placed in loops of intestine which had been tied off caused an increased secretion of fluid into the intestine. Brieger[82] further confirmed this with better methods and showed that the fluid was a real secretion, and not an inflammatory exudate, or a transudation.