The original subject suggested for this discussion was the mechanism of the action of drugs. There are, of course, many ways in which drugs act, and so wide a subject might have prevented any close consideration of progress made in a more limited field. Certain drugs, such as ephedrine, eserine, atropine and others, are known to act in relation to adrenaline and acetylcholine which are active substances present in the body. The action of other drugs, such as quinine, procaine, pethidine and antihistamine agents, is also beginning to find an explanation in their relation to adrenaline, acetylcholine and histamine.