REGENERATION OF PERIPHERAL NERVES 503 



sectional area to its control fibers than no. 106, the older animal, 

 surviving only 26 days after the operation. 



The objection may be made that the greater lapse of time 

 in the case of no. 154 accounts for its greater development in 

 size of fibers. This objection does not hold good if we compare 

 nos. 114 and 154 in which the lapse of time is greater in the 

 case of the older animal yet it fails to develop fibers as nearly 

 equal to its control as no. 154, the younger animal. 



AXIS-SHEATH AREA RELATION: NORMAL ANIMALS 



For determining the area relations of axis and sheath, series 

 of measurements were made on fibers from normal animals, on 

 fibers from the control nerve of operated animals and on fibers 

 from the proximal and the distal ends of operated nerves. 



A drawing of the magnified image of the fiber section was 

 made outlining the entire fiber and the contained axis cylinder. 

 The area of the entire fiber was first measured by the planimeter, 

 the area of the axis cylinder was then measured and the area 

 of the sheath computed. 



Referring to table 9, we see that the average sectional area 

 of axis at the proximal end of the nerve in three normal animals 

 is 71.2 square micra; the average sectional area of sheath is 61.3 

 square micra. The axis therefore constitutes 53.7 per cent of 

 the fiber. Fibers of the distal end show a slightly different rela- 

 tion. The average of the distal axes is 47.2 square micra, the 

 average of the distal sheaths is 47.3 square micra. The axis 

 here constitutes 49.9 per cent of the fiber. These data show 

 that while both the axis and the sheath taper from the proximal 

 to the distal end of the nerve, yet the axis constitutes a slightly 

 less percentage of the fiber at the distal end, that is, the pro- 

 portion of sheath has increased at the distal end. 



Combining the percentage v^alues of both proximal and distal 

 ends, we obtain the following average percentage for the area 

 relation of axis to sheath: 



Axis 51.8 per cent Sheath 48.2 per cent 



for normal unoperated animals of 135 grams average weight. 



