Retrograde degeneration in the spinal nerves.

  • Stephen Walter Ranson
Date:
1905
Catalogue details

Licence: Public Domain Mark

Credit: Retrograde degeneration in the spinal nerves. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    The number of medullated afferent nerve fibers cut in the opera- tion on a twelve-day old rat is about 1500. [The average number of medullated fibers in the dorsal roots of twelve-day old rats was found to be 1568 (p. 274); to this must be added a 10 per cent, distal excess to find the number of medullated afferent fibers in the nerve (p. 274); and from this result 13 percent, must be sub- tracted for the afferent fibers running in the uninjured ramus anterior (p. 275). This calculation gives 1500 medullated afferent fibers which would be injured at the operation.] And were all the cells associated with these 1500 fibers to drop out, the loss would only amount to 17 per cent. Or, expressed in other words, nearly three times as many cells have disappeared as can be accounted for in terms of medullated axons injured at the time of the operation. Even if we assume that all the axons ever to develop are present (partly as non-medullated fibers) at the time of the operation on the young rat, and if we let this be represented by the number of medullated afferent axons in the adult nerve, we find that even this number, which does not exceed 2500 (see p. 274) is inadequate to account for the number of degenerated cells. For the explanation of these results we are, therefore, forced to fall back upon the existence of some as yet unknown relations within the spinal ganglion. There was not sufficient disturbance of the blood supply to ac- count for the degeneration, since the artery and vein accompany- ing each root were not in any way injured. The objection that the degeneration was due to a septic infection has been answered in connection with the discussion of the technique, and against such an objection there also speaks the fact that infection could nor produce such uniform results. It might be supposed that the fact that only the dorsal branch was cut and the ventral branch left intact explained the occurrence of a partial degeneration, and that if both branches had been cut all the cells would have disappeared. This supposition is, how- ma nifestly incorrect since the intact ventral branch did not contain more than 13 per cent, of the afferent fibers (see footnote, p. 275), and hence cannot be responsible for the 48 per cent, of the cells which survive. I he results obtained by the enumeration of the medullated nerve fibers in the ventral and dorsal roots of young rats surviving two months after the section of the second cen ical nerve are much less