NATURE OF CONNECTION BETWEEN NEURONS 347 



continuity as a product of later development and as due to a process of 

 concrescence occurring between the axon terminations and the bodies of 

 the nerve-cells with which it comes in contact. It is easy to show the 

 existence of a fibrillar structure both in the nerve-cell and in the nerve 

 fibre (Fig. 148). The axis cylinder of the nerve fibre can be regarded 

 as made up of fine fibrillse embedded in an interfibrillar substance. 

 At the nodes of Ranvier the interfibrillar substance is interrupted, the 

 fibrillae alone extending into the next internode and representing the 



Ax 



. 



FIG. 148. Part of an anterior cornual 

 cell from the calf's spinal cord, 

 stained to show neurofibrils. 

 (BETHE.) 



Ax, axon ; a, b, c, dendrites. 



\ 



FIG. 149 Arborisation of 

 collaterals from the pos- 

 terior root-fibres round 

 the cells of the posterior 

 horn. (RAMON Y CAJAL.) 



continuous structure which determines the conducting power of the 

 nerve fibre. In the nerve-cell the fibrillae occupy all the space between 

 the Nissl bodies, passing from dendrite to dendrite, and many of them 

 from all the dendrites and all parts of the cell sweeping through the 

 axon hillock to form the fibrillae of the nerve fibre. The existence of 

 these fibrillar structures in nerve-cell and nerve fibre is accepted by 

 most histologists. The question, however, of the connection between 

 the fibrillae of one axon and those of the next neuron, i.e. the histology 

 of the synapse, presents much greater difficulties and has excited 



