ELECTRICAL stimulation of the nervous system at the operating table has long been used as a means both of obtaining information to guide the course of the operation in progress and of increasing knowledge of the nervous system. Countless electrical arrangements have been used for stimulation, and much valuable work has been done with extremely simple apparatus. Almost any means of delivering a shock to a nerve may be used successfully, provided the operator is thoroughly familiar with his apparatus and its idiosyncrasies. Most neurosurgeons, however, find it desirable to have some sort of apparatus which is durable and safe, and which can duplicate desired stimulating conditions at any time with a minimum of attention. The instrument here described was designed to fill such a need. The 60 cycle, approximately sinusoidal, alternating current used in power lines provides a satisfactory, if not ideal, stimulus for the majority of applications in