1906.] 



Regeneration of Nerves. 



277 



(4) Experiments on the Rate of Medullation in Regenerating Nerves. 



Another very important piece of evidence which supports our general 

 views was obtained by examining regenerated nerve-fibres in various parts 

 of their course. In the preliminary announcement of our results we 

 stated : — 



"We think in some cases that the more distant the situation from the 

 original point of section, the less perfectly developed the nerve-fibres appear 

 to be ; myelination has progressed less in the distal portion of their course." 



This conclusion was derived from the examination of a large number of 

 specimens, but as no special measurements of the distance in each case from 

 the point of section had been made, we thought it advisable to examine the 

 matter more systematically.* 



We accordingly divided the sciatic nerve of a cat high up in the thigh, 

 and sutured the two ends together. In time the resulting paralysis had 

 largely disappeared, and from this we judged that regeneration of the nerve 

 had occurred, and 84 days after the operation the animal was anaesthetised, 

 and the nerve was found to be excitable both above and below the junction 

 to a weak faradic current, such a current as could just be felt by the tongue. 

 The animal was then killed, and a piece of the sciatic nerve immediately 

 below the junction was placed in Marchi's fluid for subsequent microscopical 

 examination. A piece of the lower end of the posterior tibial at the level of 

 the ankle was similarly treated. The histological study of longitudinal and 

 transverse sections of the two portions of nerve showed a much greater degree 

 of myelination at the upper than at the lower end. 



In order to make the experiment still more exact, we proceeded in rather 

 a different way in a second experiment. A possible objection to the first 

 experiment would be that the posterior tibial is a motor nerve, and regenera- 

 tion of motor fibres is as a rule slower than that of sensory fibres ; the 

 greater amount of medullation observed at the upper end of the sciatic 

 might possibly have been due to the fact that there we were chiefly examining 

 sensory fibres. This objection does not really hold, because all the bundles 

 in the upper end of the sciatic were almost equally well myelinated. Still, it 

 appeared wise to meet the objection by somewhat varying the manner of 

 observation. The sciatic nerve of a cat was cut and sutured ; 91 days later 

 the animal was killed by chloroform, and during the anaesthesia that preceded 

 death the nerve was found to be irritable to weak faradisation as before, both 

 above and below the junction. In the dissection of the nerves, a large motor 



* We find that this observation was also made by Langley and Anderson (loc. cit., 

 p. 425). They say, " In one or two of our cases we examined the whole length of the 

 nerve and found that the medullated fibres decreased towards the periphery." 



