CH. XIV.] REGENERATION OF NERVE 151 



I may mention a few of the experimental results which have 

 come out of the renewed work elicited by the promulgation of the 

 autogenetic theory. 



(1) It is possible m entirely to prevent reunion with the central 

 ends of divided nerves. In our own work we accomplished this 

 by removing a long stretch of the main nerve experimented with, by 

 making the skin incision as small as possible, and by inclosing the 

 top end of the peripheral segment in a cap of sterilised gutta-percha. 

 Under such circumstances no auto-regeneration occurs. 



(2) Pieces of nerve may be transplanted under the skin, and in 

 time a few fully formed medullated fibres appear within the degener- 

 ated bundle of fibres. This is adduced by Kennedy as undoubted 

 evidence of auto-genesis, but, again, is easily explicable on the 

 hypothesis that the new fibres had wandered in from cutaneous 

 nerves divided in the course of the operation, and we showed that if 

 this fallacy is excluded by transplanting the nerve, not into the 

 subcutaneous tissues, but on to the stomach wall in a sheath of 

 peritoneum, where invasion by nerves is practically impossible, no 

 regeneration occurs at all. 



(3) The late appearance of the medullary sheath in those portions 

 of the regenerating fibres which are most distant from the place 

 where the nerve is originally cut and sutured, is a conclusive piece 

 of evidence that the new nerve-fibres grew from the central end in a 

 peripheral direction. 



(4) After regeneration has occurred, the nerve may be again cut 

 across, either on the central side of the original point of section (as 

 in Langley and Anderson's work), or on the peripheral side of the 

 original seat of operation (as in our own work). In the former case 

 Wallerian degeneration occurs in all the new fibres, showing that 

 they were all under the nutritive control of the cells of the central 

 nervous system In the latter case the degeneration took place 

 solely on the peripheral side of the second cut. The direction of 

 degeneration is always the direction of growth, so this experiment 

 shows that the growth of the new fibres had not started from the 

 periphery centralwards, but in the reverse direction. On looking up 

 the literature of the subject, I found that Vulpian also did this 

 experiment with the same result, and it can hardly be doubted that 

 this formed one of the factors that later led him to abandon the 

 autogenetic theory. An experiment on somewhat the same lines has 

 been carried out recently by Lugaro : he has shown that regeneration 

 of the cut nerves connected with the lower part of the spinal cord 

 does not occur after that part of the spinal cord has been extirpated. 

 This is a very striking piece of evidence, showing the dependence of 

 the growth of fibres on the activity of the cells of the central nervous 

 system with which they are originally connected, 



