The action of the sodium citrate, sulphate, fluoride, etc., when applied locally, may be inhibited by the administration of an approximately equal quantity of calcium or magnesium chloride of the same concentration. The counteraction of the effect of barium chloride, however, requires a much greater concentration of calcium. Using equal quantities of the two salts, the action of the barium is usually not inhibited, a fact which I have previously stated. With greater concentrations of the calcium chloride, the antagonistic action, however, is clear. This is shown in the following experiment: Applied locally to the intestine of a rabbit 1 c.c. m/320 BaCl_{2} solution caused active peristaltic movements. The application of 1 c.c. m/320 CaCl_{2} solution exercised no inhibiting effect whatever. The same quantity of m/40 CaCl_{2} was then poured on the loops, and a slight but distinct quieting of the loops took place. The addition of 1 c.c. m/6 CaCl_{2} caused the loops to become entirely motionless. After waiting a considerable time, 1 c.c. m/8 BaCl_{2} was poured on the intestine. Immediately violent peristaltic movements took place. Several c.c. m/6 CaCl_{2} exercised practically no inhibiting influence; while 2 c.c. ⁵⁄₈m CaCl_{2} solution suppressed the movements entirely for a short time. The question concerning the exact seat of action of the purgative salts remains still unanswered. Whether, upon being absorbed into the blood, they act on the central nervous system is not known. There is no evidence to show that this is the case. It seems certain, on the other hand, from the experiments here described, that they undoubtedly have a peripheral action either on the peripheral nervous mechanism or on the muscle cells themselves. It is impossible to prove that there is no action on the central nervous system, and at present it seems impossible to prove whether the peripheral action is directly on the nerves or on the muscles. The existence in the walls of the intestine of the ganglionic plexuses of Auerbach and Meissner must be taken into consideration; and with the methods available there seems to be no way of distinguishing the action on these plexuses and the direct action on the muscle cells. The ultimate effect is on the muscles and glands; and the fact that an entirely local ring-shaped constriction can be brought about by the local application of a drop of one of the salt solutions to the surface of the intestine would seem to indicate that only a small group of the circular muscle fibres themselves is affected. The fact that the nerve plexuses form a continuous network, and are intimately related in their various parts, would suggest that the occurrence of an action on these plexuses confined to so small an area is improbable. The discussion of the exact location of the action is, however, of relatively little importance, as compared with the main facts shown by these experiments, namely, that _it is possible to