Although many able observers have, within the last few years, investigated the physiological action of the Calabar bean, a singular amount of discordance has characterised the results arrived at. An intention, in the first place, of adding proofs in confirmation of the views advanced in an investigation published in 1862, has induced the author to reconsider the subject. The result has been that the actions of this substance have been found to be much more complicated than was at first supposed, and this may be understood when it is stated that it acts on the spinal cord and on the motor nerves, and also on the sympathetic system, and that, in this manner, it directly influences nearly all the vital functions. It is not proposed, at this time, to examine what must be regarded as the most curious action of Physostigma, that, namely, on the pupil, which results from its topical application to the eyeball or to the mucous membranes which are anatomically connected with it. The theories of this action, though some of them have been advanced by men of such eminence as Donders, Graefe, Rosenthal and Bowman, are extremely unsatisfactory. It is hoped that a distinct conception of the general physiological effects will suggest a correct explanation of the myositic action, and there can be no doubt it will assist in arriving at this conclusion.