106 



HISTOLOGY. 



distinct as we proceed from these on either side. In the node 

 itself there is a characteristic dark-brown coloration, which is 

 due to the staining of the cement substance, which is present 

 in the form of a ring-like sheath between the axis cylinder and 

 Schwann's sheath. There is thus formed with the axis cylin- 

 der a brown cross, as shown in Fig. 76. This is known as 

 the cross of Ranvier. 



If we boil medullated nerve fibres in ether or alcohol, the 

 myelin dissolves, and there remains a fine network surrounding 



Piece of a medullated nerve fibre from a frog, boiled iu absolute alcohol. In the centre 

 is the axis cylinder, and around it the neurokeratin network, x 650. 



the axis cylinder. The substance of this network has proper- 

 ties similar to those of keratin, not being affected by trypsin 

 digestion. It is for this reason known as the neurokeratin net- 

 work (Ewald and Kuhne) (Fig. 77). It is regarded by some as 

 an artifact (v. Kolliker, Ramon y Cajal). 



FIG. 78. 

 Nuclei of Henle 



\nclettN of .*"'(/( ini a ii ' > 

 ii sde 



Uenle's shviit 

 Axis cylinde 

 Medullary sheath 



of a medullated nerve fibre from the uervus radialis of man, treated with osmic acid. 

 Tim nuclei of Schwann and Henlr arc to be seen X 400. 



The /Schwann 's sheath or neurilernma is situated outside the 

 medullary sheath, and is joined with the axis cylinder at the 

 nodes of Ranvier by a cement substance. It is a very fine 

 homogeneous membrane which shows at various places in its 

 course nuclei surrounded by a small quantity of granular pro- 

 toplasm (Fig. 78). These nuclei, together with the collections 

 of protoplasm, may be termed Schwann's corpuscles. These are 



