Literary Notices. xxxv 



sheaths are developed in the peripheral segment from the neurilemma 

 nuclei of the degenerated nerve fibers. They present a text-figure, in 

 which the steps in the diff'erentiation of the neurilemma cells to nerve 

 fibers, as interpreted by them, are clearly shown. It is needless to say 

 that their interpretation of the appearances presented by the distal seg- 

 . ment of a severed nerve in process of regeneration is in direct contra, 

 diction to the observations made by investigators who have reached 

 the conclusion that regeneration of the peripheral nerves is by a down- 

 growth of central axis cylinders. The writer of the review has ob- 

 served in his own preparations many of the appearances described by 

 Ballance and Stewart, but felt justified in using them in support of 

 the central theory of nerve regeneration, since he never found evidences 

 of regeneration, in the form of newly formed axis cylinders (in prepara- 

 tions stained by the method of Stroebe), until such time as the down- 

 growing axis cylinders reached the peripheral segment. While it is 

 therefore difficult to explain the difference of results obtained and will 

 not be attempted by me, until after renewed investigation of this prob- 

 lem, attention should be drawn to the fact that the observations pre- 

 sented by Ballance and Stewart pertaining to the regeneration of 

 the degenerated portion of the central segment of a severed nerve may 

 as readily be used in support of the "central theory" as for the support 

 of the ''peripheral theory" of nerve regeneration, as is done by them ; 

 and, if used in support of the central theory, for which there is every 

 justification, it is necessary to assume that, while the newly formed 

 axis cylinders of the central segment develop as outgrowths of the cen- 

 tral axis cylinders, those of the distal segments are or may be developed 

 from the neurilemma cells, cells of mesenchymal origin, which in em- 

 brvonic development take no part in the development of the axis cylin- 

 ders, if we accept the views of the great majority of investigators who 

 have studied the histogenesis of perijiheral nerves. 



The evidence presented by Ballance and Stewart is therefore 

 not sufficient to warrant an overthrow of the views held by the majority 

 >:>{ observers, who : have investigated, the problem of regeneration of 

 nerve fibers, namely, that the newly formed axis cylinders are out- 

 growths from the central axis cylinders and that the structural elements 

 of the i)eripheral segment do not contriljUte to the axis cylinder forma- 

 tion. O. CARL HUBER. 



