420 SCIENCE PROGRESS 



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, 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 central- 

 wards, 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. Ocular evidence is, however, 

 perhaps more convincing than the description of experimental 

 results, so I will next present to the readers of Science Progress 

 drawings of some of the microscopic specimens prepared by the 

 latest improved methods. 



Cajal, by the help of his new silver method, comes to the 

 conclusion that the new formation of nerve axons in the peri- 

 pheral stump is exclusively due to growth from the central end. 



