The early responses of frog embryos to tactile stimulation

Abstract

In the course of some experiments on the regeneration of the spinal cord of frog embryos, it became necessary to establish certain facts in regard to their earfy tactile responses, as has been done for Diemyctylus and Amblystoma by Coghill. The results of this study are briefly summarized here.

The frog embryo exhibits a reaction toward the side stimulated as its first response to tactile stimulation with a fine human hair. This occurs so constantly that it must be regarded as normal for the frog, though only an occasional and aberrant reaction in the salamanders. This first response is followed by an avoiding-, a double-coil-, an S-reaction and the swimming movement, in order.

In a number of embryos, the cord was cut at different levels to determine the location in the cord where stimuli are transferred from one side of the body to the other. The results are, briefly, as follows: (1) when the cut passes through the brain, the portion anterior to the cut never responds to stimuli, while that posterior to it exhibits the usual series of reactions; (2) when the cut passes through the medulla, the same results are obtained; (3) when the cut passes through the middle of the body at a point just behind the medulla, both parts usually go through the normal series of reactions; (4) when the cut passes just anterior to the tail or (5) through the tail itself, the part of the body anterior to the cut goes through the normal series of responses, while that posterior to it remains negative. From these results it is evident that in the middle of the embryo there is a region about a millimeter in length which includes the upper part of the spinal cord and the lower part of the medulla, in which the decussations of the primary spinal nerve-paths take place, enabling the transfer of stimuli from one side of the body to the other.