QUARTERLY JOURNAL OF EXPERIMENTAL PHYSIOLOGY. single rootlet was sectioned, all the emerging fibres in it should survive.

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1 : QUARTERLY JOURNAL OF EXPERIMENTAL PHYSIOLOGY DOES A FRACTION OF CENTRIFUGAL FINE MEDULLATED FIBRES IN THE DORSAL ROOT BELONG TO COLLAT- ERALS OF THE SENSORY FIBRES? By KEN KURE and MORTO KAJIYAMA. From the Medical Clinic of the Tokyo Imperial University. (Received for publication 6th September 1935.) RECENTLY Barron and Matthews [1935 a] have come to a conclusion, through their electroneurographic study, that about 40 per cent. of the dorsal-root fibres carry centrifugal impulses. They quoted the controversies concerning the number of the spinal efferent fibres in the investigations of many previous authors, and wished to account for the discrepancies through the following hypothesis. Namely, they believed that many of the fibres that leave the cord by any given rootlet have entered by other rootlets up and down the cord and have their cell station in the posterior root ganglion, and the greater the extent of nerve section the more of the fibres leaving by this rootlet will have been cut as they enter the cord. Therefore the greater the extent of denervation the smaller the number of surviving fibres. Finally, if only a single rootlet was sectioned, all the emerging fibres in it should survive. We take an interest in the result of these authors' work on the point that they found many (40 per cent.) spinal efferent fibres in the dorsal root by an electroneurographic method. We cannot agree, however, with their hypothesis that efferent fibres are collaterals of sensory fibres, which they used to account for the discrepancies of many previous authors concerning the number of spinal efferent fibres, because we believe that the result of the authors, who found only a few spinal efferent fine fibres in the dorsal root, is due to error in technique, as was already mentioned in the previous paper. We must also stand against the hypothesis of these authors, because they said in their last paper [1935 b] that the fibres which they consider spinal efferent are different from the spinal parasympathetic fibres. If their opinion be true the spinal efferent fibres in the dorsal root account-for 80 percent. of the total fibres; this does not exist in fact. So we must deter- VOL. XXVI., NO

2 2 Kure and Kajiyama mine whether the spinal efferent fibre of Barron and Matthews belongs to the spinal parasympathetic, or are collaterals of sensory fibres. Hitherto we have published a number of papers on the existence of the spinal parasympathetic fibre in various journals, especially in this journal, and we hardly need to repeat it here. But, in order to demonstrate that at least most of the spinal efferent fibres do not consist of collaterals of sensory fibres, we carried out the following experiments. I. SERIES OF EXPERIMENTS. Experiment 1.-In one dog we sectioned the dorsal roots of the 5th, 6th, and 7th lumbar nerves on the left side, and 5th and 7th on the right side. After 10 days we stained the intact dorsal root of the right 6th lumbar nerve and the five sectioned dorsal roots by the Marchi method. We found no degenerated fibres in the remaining intact dorsal root, while we saw many degenerated fine medullated fibres in the peripheral stump of the sectioned dorsal roots. Experiment II.-In this dog we sectioned the dorsal roots of the 4th, 5th, and 6th lumbar nerves on the left, and 4th and 6th on the right side. Fourteen days later we were unable to find any degenerated fibres in the intact right 5th lumbar dorsal root, although we found many degenerated fine medullated fibres in the peripheral stump of the five sectioned dorsal roots. From the result of this series of experiments it is clear that sensory fibres in a dorsal root do not send their collaterals into neighbouring dorsal roots at a different level from that by which they enter. Barron and Matthews considered, furthermore, that the collaterals come from a long distance up and down the dorsal roots at a different level from that containing the entrant fibres. Again, in order to test this hypothesis, we carried out the second experiment. II. SERIES OF EXPERIMENTS. Experiment I.-In this dog we sectioned on both sides the dorsal roots of the 3rd, 4th, and 5th lumbar nerves. After 12 days we investigated the dorsal roots of the 9th, 10th, 11th, 12th, and 13th thoracic nerves and those of the 1st, 2nd, 6th, and 7th lumbar nerves on both sides, and were unable to find any degenerated fibre in these dorsal roots, while we observed in the peripheral stump of the sectioned dorsal roots many degenerated fibres (figs. 1 and 2). Experiment II.-We sectioned in this dog dorsal roots of the 2nd, 3rd, and 4th lumbar nerves on the left, and those of the 2nd and 3rd on the right side. Fifteen days later we investigated the dorsal roots between the 9th thoracic and 1st lumbar nerves on both sides, and the 5th, 6th, and 7th lumbar on the left, and the 4th, 5th, 6th, and 7th lumbar

3 Fine Medullated Fibres in the Dorsal Root nerves on the right side, using Marchi technique. There were no degenerated fibres in these dorsal roots, while there were many degenerated fibres in the peripheral stumps of the sectioned dorsal roots. The result of this series of experiments shows that a dorsal root does not send collaterals as spinal efferent fibres to dorsal roots a long distance up and down the cord. Besides, we investigated histologically the central stumps of all sectioned dorsal roots and found there many intact fine fibres, but none degenerated, with the exception of large fibres. Here again it is necessary to mention the results of Barron and Matthews [1935 a]. They sectioned a single dorsal rootlet of each side in 14 cats, and, having carried out electroneurographic studies after a month, they confirmed that the surviving dorsal rootlet still had activity as a normal root. Furthermore, they found many intact fibres (30-50 per cent.) in the central stump of the sectioned rootlet. They used this finding to confirm their hypothesis above mentioned, and concluded as follows: " It appears to us that of these fibres entering the cord by the posterior roots more than half send collaterals out to the periphery via a posterior rootlet different from that by which they enter." The fact that they could find almost a normal number of spinal efferent fibres in the dorsal root after section of a rootlet does not prove that most of the spinal efferent fibres are collaterals of sensory fibres. Although Barron and Matthews sectioned a rootlet, we sectioned a whole dorsal root, because we thought that an intradural section of a rootlet might possibly cause an injury to other rootlets. This point is the cause of the discrepancy between their result and ours. We do not think, therefore, it is necessary to repeat their last work. Moreover, section of all the rootlets, rather than a single rootlet of the dorsal roots, would be expected to give rise to a larger number of degenerated collateral fibres in the central stumps. We firmly believe that the hypothesis of Barron and Matthews is untenable, so far as the histological investigation is concerned. If the opinion expressed in their last paper [1935 b] be true the central stump of sectioned whole dorsal root contains but a few intact fibres. This is quite incompatible with our result, because we found always many intact fibres in the central stump of the sectioned whole dorsal root. Concerning Barron's and Matthews' finding that collaterals come from other dorsal roots at a different level, we have produced sufficient counter-evidence in this paper. CONCLUSION. The result of our investigations shows that the hypothesis suggested by Barron and Matthews from their experiments on cats is not supported 3

4 4 Fine Medullated Fibres in the Dorsal Root by our work on dogs. The results of previous authors, who found only a few spinal efferent fibres in the dorsal roots, depends perhaps upon an inadequate manipulation or method of investigation. REFERENCES. BARRON, D. H., and MATTHEWS, B. H. C. (1935 a). J. Physiol. 83, 5 P. BARRON, D. H., and MATTHEWS, B. H. C. (1935 b). Ibid. 85, 104.

5 Quarterly Journal of Experimiental Physiology, Vol. XXVI., 1936.] [PLATE 1. - b a FIG. 1. Dorsal root of the 11th thoracic nerve (II. series, Experiment 1) 12 days after section of the dorsal roots of the 3, 4, and 3 lumbar nerves on both sides. Marchistaining. a-intact fine medullated fibres. b intact large medullated fibre. b a -- FiG. 2. Peripheral stump of the sectioned dorsal root of the wth lullmbar nerve, 12 (lays after operation (Ii. series, Experiment 1). MIarchi-staining. a-degenerated fine mnedullated fibre. b intact large medullated fibre. KEN KuRt an l MORIO KAJIYAMA, "Does a Fraction of Centrifugal Fine Medullated Fibres in the Dorsal Root belong to Collaterals of the Sensory Fibres? "