These for the most part are such as act also upon the kidneys; but some few, as copaiba, and the balsams of sulphur, cubebs, buchu, and bearberry, appear, like nux vomica and its chief alkaloid (strychnia), to have a tonic effect upon the muscular layers of the bladder, aiding it to contract and expel its contents when from various causes there is difficulty in doing so.