42 



NERVOUS SYSTEM. 



point of junction of the two roots, is placed a small ganglion. 

 This ganglion is made up of a collection of cells having the 

 most different and ill-defined relations with the nerve tubes 

 distributed in it. We do not know the functions of this 

 ganglion ; we only know that it plays some part in nutrition 

 (role trophique), as discovered first by Waller, and since con- 

 firmed by Bernard and many other physiologists. When an 

 anterior root is cut, the peripheral or distal end is disorgan- 

 ized, whilst the central end is uninjured, because it is still 

 connected with its own trophic centre, namely, the spinal 

 cord. On the other hand, when a posterior root is cut be- 

 tween the spinal cord and the ganglion, the end remaining 

 in connection with the ganglion remains intact, whilst the 



Fig. 14. Changes produced in the nerves by section of the spinal roots.* 



end fastened to the spinal cord is disorganized (Fig. 14, 1 

 and 3) ; the ganglions of the posterior roots possess, then, 

 the property of trophic centres of those roots connected with 

 them, or, in other words, of the sensory nerves. Indeed, there 

 is no need of mentioning that if the mixed nerve (root ?) be 

 cut beyond the ganglion, all the peripheral or distal portion 

 is altered, the sensory elements as well as the motory ele- 

 ments (Fig. 14, 2). 



B. SPINAL CORD. 



1. Means of Conduction. The centripetal nerves return, 

 then, to the spinal cord by the posterior spinal roots ; having 



* Fig. 1. The section is made in the posterior root, above the ganglion. 

 The portion A, comprising that between the section and the- cord, alone under- 

 goes any change; the portion A, extending to the ganglion g, remains un- 

 changed', as well as the anterior root S. 



Fig. 2. The section is made of the mixed nerve, immediately below the 

 junction of the two roots. The portion A of the mixed nerve is changed, the 

 two roots (the posterior S and its ganglion g) remaining unchanged. 



Fig. 3. The posterior root is separated from the cord at A. Its peripheral 

 extremity S (turned down) undergoes no change. (Cl. Bernard.) 



