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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



degenerative changes in the non-medullated fibres information is scanty. 

 Bowditch and Warren l observed that when the sciatic nerve of the cat was 

 sectioned, degeneration of the motor and vaso-constrictor fibres in the periph- 

 eral portion went on at about the same rate. Stimulation of the peripheral 

 part of the nerve gave a vaso-dilator reaction after the vaso-constrictor reac- 

 tion had entirely disappeared, suggesting that the constrictor fibres degenerate 

 more rapidly than do the dilators, although it is not improbable that the 

 dilator fibres in this location really belong to the medullated class (Howell). 

 After five days no vaso-motor reaction at all could be obtained. In a recent 

 study, by Tuckett 2 of the degeneration of the non-medullated fibres contained 

 in the branches springing from the superior cervical ganglion, it is stated that 

 the degeneration as traced by histological and physiological methods is com- 

 plete within thirty to forty hours after section of the fibres, and that the 

 degenerative changes involve only the core of the fibres, the outside sheath 

 and nuclei being unaffected. 



Degeneration in the Central System. In the central system, the distal 

 portion of the fibres separated from the cell-body degenerate as at the periph- 

 ery, and this reaction has therefore formed a means by which to study the 

 architecture of the central system. The details of the process are, however, 

 not well understood. 



So far, then, as the principal outgrowth of the nerve-cell is concerned, it is 

 found to be always under the nutritive control of the cell-body from which it 

 springs. The changes which take place when the spinal roots are cut will serve 

 to illustrate this control (see Fig. 161). Section of the dorsal root at the distal 



FIG. 161. Schema of a cross section of the spinal cord, showing the dorsal and ventral roots and the 

 points at which they may be interrupted : D R, dorsal root ; V R, ventral root ; G, ganglion ; M, muscle ; 

 S, skin ; 1, lesion between ganglion and cord ; 2, lesion between muscles an<* cord ; 3, lesion between skin 

 and ganglion ; 4, combination of 2 and 3. 



side of the spinal ganglion at 3 causes a degeneration of all the fibres which 

 form the dorsal nerve-root distal to the ganglion. Section of the dorsal root 

 at 1 causes degeneration, central to the section, of those nerves which are out- 

 growths from the cell-bodies of the spinal ganglion. Section of the ventral 

 root at 2 causes a degeneration distal to the point of section in those fibres 

 which form the ventral root and which arise from the cells within the spinal 

 cord. In each case, therefore, the degeneration occurs on one side only of the 

 section, and that is the side away from the cell-body. 



1 Journal of Physiology, 1885, vol. vii. 2 Tuckett : Journal of Physiology, 1896, vol. xix. 



