During the last 5 years or so it has been demonstrated that the light scattered by a multifibered nerve in a bean1 of white light changes as a function of impulse propagation (Hill and Keynes, '49; Hill, '50, '50a; Bryant and Tobias, '52). Early experiments were all done using marine invertebrate nerves, and since the effect was not at first detected with frog nerve it appeared that it might occur only in certain forms and therefore be of limited interest. Also, if the phenomenon were thus restricted then work on it might be limited to marine station excursions or to experiments with animals shipped over long distances. It was of interest therefore that the phenomenon was soon found also to occur with frog nerve, but it was not further investigated in the frog at the time (Bryant and Tobias, '%2). The present communication is devoted primarily to a more detailed description of the frog nerve optical response, to the influence upon it of certain variables and to some experiments which have bearing on interpretation.
I t should be made clear that the experiments have been done
in awareness of the fact that it is not yet known horn individual axons contribute to the whole nerve optical response.
No chaiige in scattering has yet been reported to accompany activity in single isolated axons. Therefore the change in