Impulses in the Segmental Nerves of the Earthworm

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Abstract
In the segmental nerves of Lumbricus large repetitive impulses were observed in response to stimulation of proprioceptors, smaller impulses in response to epithelial stimulation by HCl, NaOH, and NaCl and still smaller ones in response to photic stimulation. The response to illumination was a gradual increase in impulses to a maximum; it was then usually interrupted by big proprioceptive impulses initiated by the muscular response. In response to tactile stimulation impulses of a range of amplitudes, rapidly adapting, and increasing in number with increasing area stimulated were observed. The rates of conduction of the majority of the tactile and proprioceptive impulses lie between 4 and 8 cm. per second. In one segmental nerve responses were obtained to homolateral stimulation of that segment and of the two adjacent segments. Exploration of this sensory field with a fine needle showed local areas from which no response was obtained. A horizontal cut through the epithelium and subepidermal plexus abolished responses dorsal to the cut; a vertical cut weakened them on either side. Responses were abolished locally by nicotine. Strychnine had no effect on the sensory field. Efferent impulses, somewhat smaller than the impulses in response to proprioceptive stimulation, passed out from the ganglion in the segmental nerves. Few proprioceptive impulses in a contraction wave arose in a segment after the nerves of the adjacent segment toward the approaching wave were cut, and none when the nerves of the second segment removed were also cut. Stimulation of one segmental nerve induced contraction of that segment and weak contraction of the two adjacent segments. Peristaltic waves were often conducted but greatly impeded after one ganglion was removed and were not conducted after two or more ganglia were removed. It is concluded that sensory and motor impulses are conducted in separate branching fibres rather than in a continuous nerve net.

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