406 ELECTRO-PHYSIOLOGY CHAP. 



the branches considerably exceeds that of the trunk, the same, of 

 course, occurs in the electrical nerve also, and Fritsch computes 

 that after giving off twenty-five branches only, the diameter of 

 the nerve is more than doubled. Although the cross-section of the 

 axis-cylinder in the medullated terminal branches is of scarcely 

 measurable proportions, the sum of the cross-sections of the collective 

 nervous processes in the plates (which swell enormously after losing 



ne 





FIG. 265. J\Inlii]iti i'ii /-H.S. One of the two yiunt ganglion-cells ; nt = axis-cyliinler process. (Fritsch.) 



the medullary sheath) must be reckoned at about 14'113 sq. mm., 

 so that if the superficies of the trunk were only 40'7l51 p the 

 total cross-section might increase (by ramifications and terminal 

 swelling) 346,760 times during its course from centre to organ. 

 This is mainly due to the increase of interfibrillar intermediate- 

 substance, although a fibrillated structure of the axis-cylinder, 

 apart from the stalk of the discs, has not been demonstrated. 



A small rounded spot may be detected, even with the unaided 

 eye, upon the long section of the spinal cord, near the origin of 



