In experiments upon paths of nervous conduction in the mammalian spinal cord, departures, both numerous and wide, from the “Fourth Law” of Pfluger have been recorded by one of us’. Pfluiger’s “Fourth Law ” runs: ” Reflex irradiation in the spinal cord spreads upwards or anteriorly, i.e. towards the medulla oblongata.”
Contrary to this statement, there certainly exist many spinal paths by which the activity aroused in spinal segments situate nearer the head is commtunicated to segments lying fuirther backward. The present paper results from search for more detailed evidenice regarding aborally-running reflex spinal paths. The above quoted “law” of Pfluiger is usually accepted and endorsed without comment, but physiological literature records here and there examples of spinal reflexes irradiating aborally.
Thus: the “trab reflex ” (Lu chsinger) in goat and cat; the “scratching” reflex (Haycraft, Goltz) in dog and rat; the “shake” reflex, mentioned by Goltz and Ewald4, in the dog; reflexes radiating from the pinna (skin supplied by 2nd cervical nerve) to neck, to forelimb, to hindlimb, and to tail (Sherrington5) in cat, dog, and monkey, and numerous similar instances furnished by the last named.
Reaarding the demonstration of intraspinal nerve-fibres disposed suitably for such conduction, i.e. to be intermediary between receptive “centres” headward and motor root-cells several segments further back, the definite information is very scanty. By the Golgi method, axis- cylinder processes from cells in the spinal grey matter have been traced to enter all the white columns (cellules des cordons, Ram6n6, van Gehuchten; Strangzellen, Kolliker), especially the ventro-lateral.
To discover in which direction these then run, i.e. whether headward or backward, is difficult. v. Lenhossek writes that he could not from his preparations decide which way they went. Ram6n 8 and van Gehuchten say that for the most part the neuraxons bifurcate at once into an ascending and a descending nerve-fibre, but that some without division turn upward, others similarly downward, and that in some instances the neuraxon divides into three fibres which all turn upward or all turn downward. It is impossible to see to what distance the fibres run along the length of the cord, i.e. what segmental interval they bridge.