570 ANNALS NEW YORK ACADEMY OF SCIENCES 



generating fibers to expand beyond the diameters of their parent fibers 

 in the cervical sympathetic trunk. The results showed no expansion, 

 and the distal fibers tended to recover the characteristics of the cervical 

 sympathetic trunk. 



DISCUSSION 



The growth of fiber diameter is part of a process of reconstitution 

 or maturation of the fibers and can be considered separately from the 

 longitudinal growth of the fibers toward the periphery. Although this 

 latter process of outgrowth has been the subject of numerous studies, 

 the diameter growth was not investigated intensively until the re- 

 search of Gutmann and Sanders^ on rabbit nerves. They described 

 a gradual increase in fiber diameter for the first year of regeneration 

 after suture, without recovery of either the maximum diameter or 

 of the bimodal fiber distribution. Our experiments confirm these 

 findings and, in addition, show that the increase in diameter con- 

 tinues beyond one year to at least 544 days. Also, at extremely long 

 times, up to 1363 days after suture, complete recovery of diameter is 

 not attained, nor is the bimodal distribution of fibers. The fact that 

 crushing allows much more rapid reconstitution of fiber diameter con- 

 firms their findings (Gutmann and Sanders^). 



The recovery of impulse conduction velocity and action potential 

 characteristics is also an important part of this reconstruction or ma- 

 turation process in regenerating nerve fibers. In fact, the proper 

 coordination of nerve functions might be impossible if their conduction 

 velocities are not regained, in spite of proper peripheral connections. 

 These combined electrical and microscopic experiments showed that the 

 conduction velocities and action potentials recover slowly, at the same 

 rates, as the fiber diameters increase. The conduction velocities were 

 actually compared to the fiber diameters of the distal stump, and the 

 same linear relationship between these two functions was found as ex- 

 pected for normal nerves, as reported by Gasser and Grundfest.^ 

 Therefore, the electrical characteristics of the regenerating outgrowths 

 in the distal stumps were found to be related solely to the reconstitu- 

 tion of fiber diameter and did not otherwise depend on the type or 

 size of the parent fiber in the central stump. Further data on the ac- 

 tion potentials from regenerating nerves have been reported by Berry, 

 Grundfest, and Hinsey.'^ 



A long delay between sectioning the nerve and subsequent suture 

 was shown to impede the usual reconstitution of fiber diameter and con- 



