A number of the group of drugs whose main action is on the organs of circulation act, in some respects, like the digitalis group, but instead of exerting their main action on the heart-muscle, their chief activity is manifest on the arteries and unstriped muscle in general. The most important of this series are ergot and the suprarenal extracts. Hydrastis and gossypium may be included in this category, but their action is much weaker.