26 



NERVOUS SYSTEM 



It might be added that in certain little trunks, isolated from the 

 great sympathetic nerve system, the number of these pale fibres is so 

 large, and the number of tubes with medullary substance so small, we 

 are obliged (especially in the splenic nerves} to consider Remakes 

 fibres as true nerve fibres. 



If these prolongations of the nerve globules are followed 

 up carefully, the nerve tubes will be observed, after a shorter 

 or longer distance, to be connected, in fact joined, with a 

 neighboring or a distant globule, or sometimes with several 

 of these. Thus in the spinal cord there are globules whose 

 ramifications connect them with other globules. Sometimes 

 the nerve fibres, on the other hand, terminate in muscles 

 (inotorial end-plates), or even in organs which are at present 

 but problematical (tactile bodies), and which are specially 

 found in the skin. It may also be noticed that generally 

 nerve fibres are only commissures or bridges projecting from 



These constrictions, placed at distances varying according to the 

 dimensions of the tubes, enclose segments 

 which are called interannular segments. Each 

 of these appears to represent a cell; indeed, 

 in the centre of each, and on the inner sur- 

 face of the substance of Schwann is found a 

 flat oval nucleus (Fig. 9) floating in a sea of 

 protoplasm, with which the tissue is lined. 

 Farther in is found the my dine, which, con- 

 sidered in regard to general morphology, 

 bears the same relation to the interannular 

 segment as the fat in an adipose cell does to 

 the cell. The signification of the cylindri- 

 cal axis, which runs uninterruptedly through 

 the whole series of segments, has not yet 

 been definitely ascertained from the stand- 

 point of general morphology. The study 

 of the degeneration of the nerves after sec- 

 tion, seems to confirm the foregoing conclu- 

 sions as to the nature of the interannular 

 segments, without, however, yielding us any 



Fig. 9. Nerve tubes, ac- m0 re precise information as to the nature 

 .^ iei ' 8re " of the axis cylinder, which is, notwith- 

 standing, the essential element of the nerve 

 Indeed, it seems probable that the other appearances are 



simply due to the artificial methods used in the preparations. 



* A, Nerve tube under low magnifying power, a, Constriction, b, Nucleus 

 of interannular segment, c, Axis cylinder. B, The constriction and part of 

 interannular segment, seen under a higher power (prepared with osmic acid). 

 a/, Constriction, b', Nucleus in segment. </, External nucleus in sheath. 



tube. 



