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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



vaso-constrictor fibres in the peripheral 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 reaction had entirely disappeared, suggest- 

 ing 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 1 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 complete 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 un- 

 affected. 



In the central system, the distal portion of the fibres separated from the 

 cell-bodv degenerate, as at the periphery, 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 clear. 



Nutritive Control. — 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. 85). Sec- 





Fig. 85.— 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 and cord ; 3, lesion between skin 

 and ganglion; 4, combination of 2 and :;. 



tion of the dorsal root at the distal 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 an' outgrowths 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. Tn each case, therefore, the 

 necessary degeneration occurs on the side of the section away from the cell- 

 body. The fraction of the neurone on the other side of the section may also 

 degenerate under certain conditions, but the degeneration is not inevitable. 2 



'Tuckett: Journal of Physiology, 18%, vol. xix. 



2 Kre£in:inn : Arbeiten aua <l<-m TnstUulJiir Anatomic and Physiologic des CentrcUneriiensystems 

 an der Wiener Universitat, 1892-93. 



