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Some years ago it was observed (Acheson, Lee & Morison, 1942) that cutting the phrenic nerve caused, over a period of 3 weeks, a progressive central block of the transmission of nerve impulses from the respiratory centre to the axons of the cut phrenic nerve. At that time a similar phenomenon was noted in the inferior mesenteric ganglion: section of the hypogastric nerve caused a progressive block of the transmission of preganglionic volleys to the postganglionic axons of the cut hypogastric nerve (Acheson, 1952). This phenomenon was independently discovered in the same site by Brown, McLennan & Pascoe (1952). These authors have aimed their experiments chiefly at the mechanism of the block (Brown & Pascoe, 1954;McLennan, 1954). The present paper reports experiments in which the temporal course of the phenomenon was systematically studied. Campbell, Mark & Gasteiger (1949) and Downman, Eccles & McIntyre (1953) have studied a parallel phenomenon which occurs in motoneurones when ventral roots have been cut and dorsal root axons are stimulated. METHODSCats of either sex weighing from 1-5 to 3.5 kg were anaesthetized by the intraperitoneal injection of pentobarbitone sodium (30-40 mg/kg). With aseptic precautions the abdominal cavity was opened, and the right hypogastric nerve was sectioned about 3 cm away from its ganglion. The left side remained untouched, to be used as a control. In some experiments the colonic nerve from the right inferior mesenteric ganglion was also cut; the results to be reported were not different in the experiments in which the colonic nerves were cut. The abdominal wall was closed, and the animals were allowed to recover. At intervals ranging from 2 to 180 days after the operation, under the same kind of anaesthesia the abdominal viscera were removed. A cannula in the femoral vein was employed whenever intravenous injection of drugs was necessary. The preganglionic trunks of both inferior mesenteric ganglia were dissected and placed together on a single pair of silver electrodes for stimulation, while the hypogastric nerves, after dissection, were laid separately on two symmetrical pairs of silver recording electrodes (Fig. 1). The responses of the two hypogastric nerves to stimulation of the preganglionic trunks by supramaximal rectangular

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Local tetanus limited to one leg was studied in cats after intramuscular injection of tetanus toxin. 1. The electric and mechanical response of the affected muscle after a single stimulus to the intact sensory-motor nerve is greater in amplitude and duration than the response of the corresponding muscle of the unaffected leg (Fig. 1). 2. This augmented response of the muscle is associated with an augmented response arising from the ipsilateral portion of the spinal cord, while the contralateral part of the cord is unaffected, as demonstrated by electrographic records from the motor nerves (Figs. 2 to 5). 3. The augmented muscular response is abolished when the reflex arc is broken, but the augmented response in the spinal cord is independent of changes in the muscle, the neuromuscular junction, the afferent and efferent peripheral nerves, and the dorsal root ganglia. 4. The augmented spinal response develops in the absence of the peripheral signs of local tetanus. Hence the pathogenesis of the altered state in the spinal cord is independent of the peripheral effects of the toxin. 5. In local tetanus, therefore, the toxin injected intramuscularly acts selectively upon the segments of the spinal cord which supply the innervation of the injected area. 6. The augmented spinal response may be prevented by section of the nerve trunks supplying the area of injection prior to the injection of the toxin. 7. It is concluded that in local tetanus the toxin is carried to the spinal cord by way of peripheral nerves.