250 Regeneration. 



axis-cylinders meanwhile undergoing subdivision. It is a striking 

 phenomenon in this process that the newly formed fibres of a divided 

 nerve should grow into the original areas of distribution. The 

 opinion most nearly explaining this assumes that the old paths of 

 distribution persist as actually empty tubes, or as the neurolemma 

 tubes of Schwann containing merely a softened fatty detritus, and 

 that the sprouts of axis cylinder substance find here the line of least 

 resistance in their penetration. It has, however, been shown that 

 after resection the nerve-sprouts, in spite of the insertion of special 

 interfering objects, follow along their original direction; and the 

 interesting experiments of Forsmann show that the nerve stump 

 will not invariably push its way into empty glass tubes which have 

 been inserted but will on the contrary always force its sprouts into 

 glass tubes containing nerve or brain substance, even if these be ar- 

 ranged in the wrong direction. It seems probable therefore that 

 chemotactic force, exerted by the degenerating nerve matter of the 

 peripheral portion of the nerve, determines the line of extension of 

 the growing nerve fibres (neurotropism). 



The force of growth of the central stump is usually very marked. 

 V'anlair succeeded in enclosing calcareous tubes, made of bone, be- 

 tween the two ends of a divided nerve, and the growing sprouts not 

 only found their way into the lumen of the tubes, but even into the 

 Haversian canals (Thoma). Sometimes the budding axis cylinders 

 form tumor-like masses in the scar tissue around the stump, the so- 

 called amputation neuromata. 



As the neurolemma with its nuclei remains intact in the degen- 

 erated peripheral fibres, it is possible that the formation of new 

 medullary substance may arise from this source in case the new 

 axis cylinders grow into these preformed paths. Proliferative phe- 

 nomena in the cells of the neurolemma have been actually observed 

 (Eichhorst, L. Mayer, v. Bi^ingner), and consequently the view is 

 held that this sheath, by dififerentiation of its protoplasm, may give 

 rise in segments to the axis cylinder and medullary sheath ; that 

 in this way from the old sheath new nerve fibres may be formed, 

 the segments then growing together to form continuous threads. 



Ganglionic cells and the massive nervous tissue of the brain and 

 cord are incapable of regeneration. It is well known from numer- 

 ous experiments upon animals and studies in man in connection 

 with injuries, partial ablations and other types of loss of substance, 

 as from haemorrhage, degeneration, etc., that even in case the usual 



