Jcxviii Journal of Comparative Neurology. 



performed the function of axis-cylinder formation again assume the role 

 of mesenchymal cells and develop into neurilemmal sheaths. Simple 

 and complex tissues, injured mechanically or by chemic agents, follow, 

 if regeneration ensues, the steps traversed by the respective tissues in 

 their normal development and differentiation. That there should exist 

 such wide departure from this general rule in the case of regenerating 

 nerve fibers seems problematical and can not be conceded without 

 further substantiation. 



The majority of investigators who have studied this problem have 

 recognized "the young neurilemma cells," but have not found sufficient 

 evidence to warrant endowing them with neuroblastic function. Flem- 

 ing states that the Stroebe method did not give satisfactory results un- 

 til paraffin sections (which can be cut thinner) were used in place of 

 celloidin sections. It may be stated that Huber, in an investigation on 

 nerve regeneration published some eight years ago (Journal of Morph- 

 ology, Vol. XI), modified the Stroebe method in the same direction, 

 and in all his experiments saw no evidence of peripheral regeneration. 

 Fleming further states that an amputation neuroma is not developed 

 solely by neuroblastic formation, "because if a large neuroma is so 

 formed it would necessarily mean that neuroblasts extended so far 

 downward, below what might be called their proper sphere of action, 

 that the neuroblast must be supposed to have almost acquired a malig- 

 nant tendency and ought to infiltrate muscle and other neighboring tis- 

 sues." The reviewer finds it still more difficult to explain by the peri- 

 pheral theory the regeneration of the peripheral portion of a nerve from 

 which a segment measuring 6 to 8 cm. had been removed, the space 

 between the cut ends being bridged by a cat-gut bundle or by a bone 

 tube. In experiments of this kind, naked axis-cylinders were found in 

 the loose connective tissue replacing the absorbed cat-gut or bone tube, 

 and no new axis-cylinder.=; were found in the peripheral portion until 

 the downward growing axis-cylinders developing from the central fibers 

 reached the peripheral end. 



Further in reg.enerating nerve fibers stained by the intra-vitam 

 methylen blue method, very fine axis-cylinders are found in the peri- 

 pheral segment which end at various levels, only a few in the earlier 

 stages of regeneration and a larger number in the later stages. Accord- 

 ing to the central theory, this fact is readily explained; according to the 

 peripheral neuroblastic theory, an explanation is more difficult. A 

 reason must be given for the fact that certain axis-cylinders in the peri- 

 pheral segment regenerate and others do not; and also that certain of 

 the regenerating fibers extend further down the peripheral segment 

 than do others. 



