Abstract
In observations on the amplified spike of the most excitable fiber in the branch of the peroneal nerve supplying the medial aspect of digit IV of Rana pipiens it was found that cold increased the current strength required to stimulate by virtue of its action on excitability rather than on resistance, and prolonged both the ascent and the descent of the spike, the descent, however, very much more than the ascent. Cold also increased the height of the spike and the duration of the absolutely refractory period. It is possible, however, that the latter result was referable to an artifact, and does not necessarily contradict the view that spike and refractory period are coterminate under all conditions.