Key points are not available for this paper at this time.
The present paper deals with the development of an apparatus for delivering controlled electric stimuli, and with an attempt to discover which physical aspect of 60 cycle alternating current (voltage, amperage, or wattage) is most closely related to discrimination of shock stimuli in psychological experiments.' Shock, of course, has been the most widely used, and the most type of noxious stimulus for many psychological studies. However, convenient should be italicized for, while shock is usually rather simple to apply, accurate control of the most effective physical aspect of this stimulus is difficult. A survey of the literature indicates that control of voltage alone in psychological studies is quite unsatisfactory. This is frequently the case even when considerable physical resistance is added to the circuit in series with the biological materials. Problems relating to the use of electric shock stimuli were considered in a round-table discussion of the American Psychological Association (2, 3). Although there was no close agreement among members, the general opinion seemed to be that amperage was the physical aspect of shock which should be controlled. Muenzinger and Walz (4) developed a method for controlling D.C. current (to a great extent) despite variations in skin resistance. This technic has proved quite satisfactory for a number of purposes. However, the few psychophysical experiments that have been performed with control of amperage have yielded disparate results. Thus, Dalziel and Lagen (5) found that the integumental threshold for 60 cycle alternating current was 1.1 milliamperes (ma.), while Forbes and Bernstein (6) found great fluc-
Hill et al. (Thu,) studied this question.