SIX FIGURES
As compared to the studies of electrical, metabolic and thermal parameters of function in nerve, relatively little has been done explicitly to characterize activity in terms of ultrastructural changcs which may occur hen the cell goes from the resting to the active state and then recovers again. The reasons for this disparity stem from the facts (1) that the propagated disturbance is short lived, ( 2 ) that it probably produces cheniical and ultrastructural changes which are at or beyond the limits of detection by orthodox methods, and (3) that a t any region on the axone many of the changes which it produces are probably more o r less completely reversed as the impulse sweeps by. The indirect iiieiliod of studying clieriiical and structural changes under spatially separated polariziiig electrodes, in a n attempt to bypass these difficulties, based on the assumption that the impressed potentials may, to R degree, mimic certain aspects of the cathodal and anodal phases of the propagated disturbance, has been used in this laboi-atory, but with the understanding that any extrapolation to the propagating impulse would be hazardous and could be misleading. While one finds changes occurring under such electrodes, the insensitivity of detector devices used in the past has required high voltages, relatively intense currents and long times to make them detectable, and sincc 'This work has been aided in part by a grant from the United States Public EIealth Serviee, Neurological Diseases and Blindness Institute, and in part by a grant from the Dr. Wallace C. aiid Clara A. Abbott Memorial Fund of the Uniiersity of Chicago.