THE NERVE FIBER 



135 



'B 



1- 



n 



latter is ruptured flic myelin exudes A 

 in the form of 'myelin drops.' The 

 mi/ el in, thus obtained possesses the 

 physical properties of a fat. It is 

 also capable of being blackened by 

 osmium tetroxid. By extraction with 

 ether the myelin can be removed, leav- 

 ing behind a supporting framework 

 of neurokeratin. The function of 

 myelin is probably nutritive, though 

 it has been regarded as an insulating 

 substance. It is thought to be present 

 in small a 11 101 nits even in so-called 

 non-medullated fibers. It seems rea- 

 sonable to suppose that it may have 

 a double function, that is, nutritive 

 and in part insulating. 



At frequent intervals in the course 

 of the nerve fiber its myelin sheath 



*/ 



suffers complete interruption, thus 

 forming the annular constrictions or 

 nodes of Eanvier. At these points the 

 neurolemma dips in until it is in con- 

 tact with the axis cylinder. Both axis 

 cylinder and neurolemma are contin- 

 ued past the node without interrup- 

 tion. 



The successive nodes of Ranvier 

 divide the nerve fiber into internodal 

 segments. Within each internodal 

 segment the medullary sheath, on 

 blackening with osmium tetroxid, 

 presents clear intervals which pene- 

 trate the myelin sheath in such man- 

 ner as to give the appearance of 

 obliquely disposed clear lines or inci- 

 sions. These inciftures of tf dim id I 

 (Schmidt-Lantennann lines) have 



not been satisfactorily explained and can not be demonstrated in the 

 living fiber, yet they present a constant form and are always present in 

 10 



FIG. 148. NERVE FIBERS. 



A and B, from the sciatic nerve of a 

 rabbit, isolated by teasing, and viewed 

 in profile; C, a group of nerve fibers in 

 transection, from the sciatic nerve of 

 a dog. a, axon; b, neurolemma pro- 

 jecting beyond the torn end of the 

 fiber; d, nucleus; h, endoneurium or 

 fibrous sheath of Henle; I, Schmidt- 

 Lantermann lines; n, nodes of Ran- 

 vier. Osmium tetroxid. A and B, 

 X 670; C, X 900. 



