xxxii Journal of Comparative Neurology. 



ond day after section, the parent cells dividing in an obliquely longitu- 

 dinal plane. Mitotic figures are not described nor shown in the plates 

 (Observations of Bunger and Hurer). The newly formed neurilemma 

 cells assist in the removal of the "fatty debris of the medullary sheaths 

 and axis cyHnders." By the end of the second week, the neurilemma 

 cells develop into elongated cells and these proceed to send out fine 

 protoplasmic processes from the opposite poles, well seen during the 

 fourth and fifth weeks after section; similar appearances are seen in 

 the distal segments of severed nerves not sutured. These elongated cells 

 with polar processes are said to fuse to form the new nerve fibers. In 

 the following brief statement is given a summary of the observations 

 made pertaining to the relation of the neurilemma cells to the newly 

 formed nerve fibers, which maybe quoted in full: "The more the 

 specimens are studied the more is the conclusion forced on the mind of 

 the observer that for the regeneration of peripheral nerve fibers (not 

 only the axis cylinders, but also the medullary and neurilemma sheaths) 

 the activity of one variety of cells and of one variety only is responsible. 

 That cell is the neurilemma cell." 



Ballance and Stewart unhesitatingly declare their adherence to 

 the peripheral theory of nerve regeneration, which is, that the axis- 

 cylinders, medullary and neurilemma sheaths are developed from the 

 neurilemma cells of the degenerated nerve fibers. The processes of 

 regeneration, as observed in the proximal and distal segments of a 

 severed nerve are, according to these observers, essentially the same ; 

 the differences observed are "differences of degree and not of kind," 

 since, as has been stated, regeneration of the axis cylinders and medul- 

 lary sheaths occurs in the distal segment of a severed but unsutured 

 nerve, but the newly formed nerve fibers do not attain their full ma- 

 turity until they are joined to those of the proximal end. Certain of 

 the conclusions reached by Ballance and Stewart seem warranted 

 by the appearances presented by their preparations, which are fully dis- 

 cussed and abundantly figured in this monograph ; others, however, 

 appear to me not so well grounded, since the appearances presented by 

 certain of their preparations admit, it is believed, of different interpre- 

 tations than are given them by these observers ; these latter observa- 

 tions may engage our attention primarily. The statement is made that 

 the neurilemma cells of the degenerated portion of the proximal end of 

 a severed nerve assume neuroblastic function and "secrete short seg- 

 ments of axis-cylinders and medullary sheaths," these forming the iso- 

 lated groups or colonies of newly formed nerve fibers, seen m prepara- 

 tions stained after Weigert's myelin staining method and Stroebe's 



