viii CONDUCTIVITY AXD EXCITABILITY OF XKltVE S7 



traverse the spinal cord without interruption from ganglionic 

 elements. 



These facts respecting conductivity of excitation within the 

 nervous centres suggest important conclusions as to the ana- 

 tomical arrangement and reciprocal relations of the conducting 

 paths. Starting with the fact that every nerve-fibre is connected 

 inside or outside the central organ with at least one ganglion-cell 

 (its parent -cell), it may be assumed that every reflex arc is 

 built up of nerve -cells, and that these (especially the motor 

 cells) are under the most favourable conditions for mutual 

 conduction. 



Histological investigation has so far contributed very in- 

 adequate support to this physiological postulate. It was indeed 

 natural to regard the great multipolar ganglion -cells of the 

 anterior horn, along with their numerous ramified " protoplasmic 

 processes," and Deiter's axis -cylinder process passing directly 

 into an anterior root - fibre, as the elements through which 

 the functionally distinct nerve -fibres from the periphery are 

 anatomically related at the centre. This view is expressed in 

 Gerlach's theory, which represents the protoplasmic processes 

 of the ganglion -cells as forming a rich network of the finest 

 nerve-fibrils, connecting the cells of the anterior horn not merely 

 with one another, but also with the posterior root-fibres, which 

 also, according to Gerlach, terminate in a fine fibrous network 

 after their entrance into the gray matter. Eecent researches into 

 the finer structure of the nervous centres (Golgi, Ramon y Cajal, 

 Kolliker, Retzius, and others) have substantially modified the 

 earlier doctrine of Gerlach in certain important physiological 

 particulars. There is no proof of a central nervous network, as 

 the anatomical substrate of irradiation of excitation. The cell- 

 processes (nerve-fibres) which arboresce within the gray matter 

 seem all to terminate freely, without anastomosing with the 

 processes of other nerve-cells. Certainly it can only be said at 

 present that no anastomosis has yet been detected ; its non- 

 existence may be questioned, in view of the wealth of ramifications 

 exhibited by the protoplasmic processes. Golgi indeed denied 

 the " nervous " nature of these processes, but his opinion must be 

 disallowed, since in many cases all the processes are of the same 

 character, and the nerve-fibre may even (as in the giant electrical 

 ganglion-cells of Malaptci-urm} spring, not from the body of the 



