414 SCIENCE PROGRESS 



and so reach their destination by a new channel. There is 

 absolutely no recovery if the division of the spinal cord is 

 complete, for then all possible channels are equally blocked. 



In a nerve, recovery will occur if the division is absolute, 

 and in this case restoration of function is due to the regenera- 

 tion of the nerve fibres. It is the object of this paper to 

 describe the manner in which this regeneration occurs. 



Nearly every one has suffered at some time from minor 

 injuries in the way of skin wounds, and has doubtless for a 

 time experienced anaesthesia or loss of sensation on one side 

 or other of the cut. Some months later sensation returns, 

 and the accident is forgotten. Regeneration of the nerves 

 necessary for this usually occurs without any surgical aid, and 

 and all that remains is a scar. Scar tissue, or cicatricial tissue, 

 as it is technically termed, is a dense kind of connective tissue 

 somewhat stronger and firmer than the ordinary skin. This 

 same kind of tissue is formed in the repair of all injured 

 structures in the body. When, for instance, a muscle or a 

 tendon is cut across, the formation of cicatricial tissue to bridge 

 across the gap is quite sufficient to restore the continuity and 

 uses of the injured organ. If a rope is divided, it does not 

 matter what sort of material — silk, hemp, or cotton — is used to 

 tie the ends together ; if the repairing material is sufficiently 

 strong the rope is as good as ever. So it is with the haulage 

 mechanism of the body : a tendon or a muscle can pull upon 

 the bones quite as well as before the accident, even although 

 the repairing tissue is not identical with that which was injured. 



But the case of a nerve is different. If a telegraph wire 

 is divided the repairing material must be wire, or at least 

 something capable of conducting electricity. The molecular 

 change transmitted along nerve fibres, and which is termed a 

 nervous impulse, is so peculiarly the property of nerve fibres, 

 that no amount of scar tissue is efficacious in restoring function. 

 Nerve fibres must be mended by nerve fibres and by nothing 

 else. Indeed, a large amount of cicatricial tissue is harmful, for 

 its very density is an obstacle to the successful growth of the 

 new fibres which ultimately penetrate it. 



We must never push the telegraphic simile too far in dealing 

 with the nervous system, useful as it is in talking of such 

 matters to students. If a telegraph wire is broken, all that 

 is necessary in healing the damage is to connect the ends 



