Abstract
One of us 1 has reported “small but definite electrical changes” in the optic nerve of Limulus polyphemus when the eye is exposed to light. The present communication continues this study with improved methods which have made it possible to record impulses in single fibres of that nerve, by means of a battery coupled amplifier and Matthews' oscillograph.
The compound lateral eye of Limulus is an admirable preparation for the study of photoreception. Each of the large and widely spaced ommatidia is supplied with one nerve fibre which runs directly to the central ganglion. In the eye itself there is no evidence of either ganglion cells or neural interconnections. The optic nerve is easily obtained and the eye, together with a centimeter or more of optic nerve attached, may be excised and will survive 8 hours or longer.
Action potentials from the whole nerve were studied in the young animal. When the eye is illuminated there is developed a succession of slow potential changes, superimposed on which are the typical rapid changes associated with the conduction of nerve impulses. In the whole nerve these impulses are quite irregular and resemble the responses recorded from the optic nerve of Conger vulgaris by Adrian and Matthews. 2
A study of the discharge of impulses from a restricted number of sense cells is made possible by the circumstance that the optic nerve of Limulus contains little connective tissue, and hence can be separated into bundles containing only a few fibres. Moreover, in the adult animal it appears that many of the ommatidia are no longer functional, and it frequently happens that in a small bundle separated off from the whole optic nerve there is only one active fibre.
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