NERVE 



693 



the last remnants of the myelin may not be absorbed for 

 months. In the degenerated nerve (cat's sciatic) the per- 

 centage of phosphorus undergoes a diminution from about 

 the third day. About the eighth day the loss of phosphorus 

 i.e., of the phosphatides (lecithin, kephalin) is markedly 

 accelerated, coinciding with the appearance of a strong 

 Marchi* staining reaction. By the twenty-ninth day the de- 

 generated nerve is practically devoid of phosphorus. A pro- 

 gressive increase in the water and a diminution in the total solids 

 also culminate about the same time (Mott and Halliburton). 

 In the portion of the nerve-fibre still connected with the nerve- 

 cell the degeneration only extends as far back as the next node 

 of Ranvier, and seems to be due to the direct effect of the injury. 

 In non - medullated 

 fibres, such as the 

 fibres arising from 

 the cells of the su- 

 perior cervical gan- 

 glion (Tuckett), the 

 degeneration is con- 

 fined to the axis- 

 cylinders. It begins 

 in about twenty-four 

 hours after section, 

 and the loss of ex- 

 citability and con- 

 ductivity is complete 

 by the fortieth hour. 

 It follows from 

 what has been said 

 as to the position of the cells of origin of the root fibres of the 

 spinal nerves that section of the anterior root causes degenera- 

 tion on the peripheral, but not on the central side of the lesion, f 

 Only the anterior root fibres in the mixed nerve degenerate. 

 Section of the posterior root above the ganglion causes degene- 

 ration of the central stump, but not of the portion still con- 

 nected with the ganglion, nor of the posterior root fibres below 

 the ganglion or in the mixed nerve. Section of the posterior 

 root below the ganglion causes degeneration of the fibres of 

 the root below the section and in the mixed nerve, but not 

 above it. 



* The chief constituents of Marchi's solution are potassium bichromate 

 and osmic acid. It stains medullated nerve-fibres black in the earlier 

 stages of degeneration. 



f A few fibres in the peripheral stump of the anterior root do not 

 degenerate, and a few fibres in the central stump do. These are the 

 ' recurrent fibres/ whose course is described on p. 791. 



FIG. 257. DEGENERATION OF SPINAL NERVES AND 



THEIR ROOTS AFTER SECTION. 

 The shading shows the degenerated portions. 



