TRAUMATIC AND FATTY DEGENERATION. 



539 



part of the nerve and its branches, including the sensory and motor fibres, degene- 

 rate completely (fig. 378, A), while the central parts of the nerve remain unaltered. 

 If the anterior root of a spinal nerve alone be divided before it joins the posterior 

 root, all the peripheral nerve-fibres connected with the anterior root degenerate 

 (fig. 378, B), so that in the nerve of distribution only the motor fibres degenerate. 

 The portion of the nerve-root which remains attached to the cord does not 

 degenerate. If the posterior root alone be divided, between the spinal cord and the 

 ganglion, the effect is reversed, the part of the nerve-root lying between the section 

 and the spinal cord degenerates, while the part of the nerve connected with the 

 ganglion does not degenerate (fig. 378, C). The central fibres degenerate because 



ABC 



Fig. 37S. 

 Diagram of the roots of a spinal nerve, showing the effect of section (the black rarts represent 

 the degenerated parts). A, section of the nerve-trunk beyond the ganglion ; B, of the 

 anterior root, and C, of the posterior ; D, excision of the ganglion ; a, anterior, p, 

 posterior root ; g, ganglion. 



they are separated from the ganglion. If the ganglion be excised, or if separated, 

 as in fig. 378, D, both the central and peripheral parts of the posterior root 

 degenerate. These experiments of Waller show that the fibres of the anterior and 

 posterior roots are governed by different centres of nutrition or "trophic centres.'"' 

 As the anterior root degenerates when it is separated from the cord, and the 

 posterior when it is separated from its own ganglion, it is assumed that the trophic 

 centre for the fibres of the anterior root lies in the multipolar nerve-cells of the 

 anterior horn of the grey matter of the spinal cord, while that for the fibres of the 

 posterior root lies in the cells of the ganglion placed on it. The nature of this 

 supposed trophic influence is entirely unknown.] 



Traumatic and Fatty Degeneration. Both ends of the nerve at the point of section imme- 

 diately begin to undergo "traumatic degeneration." (In the frog on the 1st and 2nd day.) 

 After a time neither the myelin nor axis-cylinder is distinguishable (Schiff). According to 

 Engelmann, this condition extends only to the nearest node of Ran vie r, and afterwards the so- 

 called " fatty degeneration " begins. The process of il fatty'" degeneration begins simultane- 

 ously in the whole peripheral portion ; the white substance of Schwann breaks up into masses 

 (fig. 377, A), just as it does after death, in microscopic preparations; afterwards, the myelin 

 forms globules and round masses (B), the axial-cylinder is compressed or constricted, and is 

 ultimately broken across (C) in many places (7th day). The nerve-fibre seems to break up into 

 two substances one fatty, the other proteid in constitution, the fat being absorbed (S. Mayer). 

 The nuclei of Schwann's sheath swell up and proliferate (D until the 10th day). According 

 to Ranvier, the nuclei of the interannular segments and their surrounding protoplasm 

 proliferate, and ultimately interrupt the continuity of the axis-cylinder and the myelin. They 

 then undergo considerable development with simultaneous disappearance of the medulla and 

 axis-cylinder, or at least fatty substances formed by their degeneration, so that the nerve-fibres 

 look like fibres of connective-tissue. [According to this view, the process is in part an active 

 one, due to the growth of the nerve-corpuscles breaking up the contents of the neurilemma, 

 which then ultimately undergo chemical degenerative changes.] According to Ranvier, 

 Tizzoni, and others, leucocytes wander into the cut ends of the nerves, and also at Ranvier's 

 nodes, insinuating themselves into the nerve-fibres, where they take myelin into their bodies, 

 and subject it to certain changes. [These cells are best revealed by the action of osmicacid, 

 which blackens any myelin particles in their interior.] Degeneration also takes place in the 



