THE RAT ELECTRORETINOGRAM. II. BLOCH'S LAW AND THE LATENCY MECHANISM OF THE B-WAVE.

Electroretinograms were obtained from the all-rod eye of the rat with uniform illumination of the entire retina and stimulus flashes of less than 3 msec. duration. Bloch's law of temporal summation was verified for the b-wave latency by varying the time between two equal intensity flashes and observing that no change occurred in the latency when measured from the midpoint of the two flashes. The results of this and other experiments are described in terms of a simple but general model of the latency-determining mechanism. It is shown that this latency mechanism acts as if it depends on a linear additive process; and also that a hypothetical excitatory substance which triggers activity in the sources of the b-wave must accumulate rapidly in time after the flash, approximately as t(8). The rate at which this substance accumulates is accurately represented by the diffusion equation for more than 4 to 6 log units in the flash intensity. This suggests that the rate-determining step in the latency mechanism may be diffusion-limited.