CENTRAL NERVOUS SYSTEM. 633 



stances or in zymotic diseases, the nervous system and especially the cell-bodies 

 are affected early and in a profound manner. 1 



With the establishment of these facts concerning the cell-body the question 

 at once arises whether the nerve-fibres are in a like mariner altered as a result 

 of their activity. 



The matter has been tested in this way : In a cat or dog a nerve-trunk was 

 stimulated by a measured induction current, and the contraction of the muscle 

 controlled by it, recorded. The physiological connection between the nerve and 

 muscle was then interrupted by the giving of curare and the nerve was teta- 

 nized. 2 The stimulation of the nerve-trunk was continued in some cases for 

 five hours. On the complete disappearance of the curare effects, a stimulus 

 similar to that employed in the first instance was found to produce muscular 

 contraction, thus showing that the continuous stimulation of the nerve-trunk 

 during this interval had not seriously diminished its power to transmit the 

 nerve impulses aroused in it. 



Histological changes have also been sought for in the nerve-fibres after 

 prolonged stimulation, but thus far they have not been demonstrated. Chemi- 

 cal changes in the nerve-fibres, if present, must be extremely small, and the 

 thermal variations which occur amount to less than 0.0005 C., or, in other 

 words, are not demonstrable. 3 Histological and chemical changes due to 

 activity have therefore been seen in the cell-bodies alone. 



Degeneration and Regeneration of Nerve-elements. All parts of a 

 nerve-cell are under the control of that portion of the cell-body which con- 

 tains the nucleus ; in this respect the nerve-tissues are similar to other tissues 

 which have been studied, and in which the nucleated portion of the cell is 

 found to be the more important. It was shown by Waller 4 that a nerve- 

 fibre belonging to the peripheral nerves when separated from the cell of which 

 it was an outgrowth soon degenerated from the point of section to its final 

 distribution. The process is often designated as Wallerian degeneration. 

 According to recent studies on this subject, 5 this degenerative change occurs 

 practically simultaneously along the entire length of the portion cut off. The 

 changes following the section consist in a fragmentation of the axis-cylinder 

 followed by its disappearance, enlargement and multiplication of the nuclei 

 of the medullary sheath, and absorption of the medullary substance, so that 

 in the course of the fibres there is left at the completion of the process the 

 primitive sheaths together with the sheath-nuclei. In the early stages of this 

 process the medullary sheath, moreover, undergoes some changes, the result of 

 which is that it stains more deeply with osmic acid, and hence appears very 

 black in comparison with the normal fibres about it (Marchi). 



Degeneration of Non-medullated Fibres. Concerning the progress of 



1 Schaffer : Ungarisches Archiv fur Medicin, 1893 ; Pandi : Ibid., 1894 ; Popoff : Virchoufs 

 Archiv, 1894 ; Tschistowitsch : Petersburger medicinische Wochenschrift, 1895. 



2 Bowditch : Archiv fur Anatomie und Physiologic, 1890. 



3 Stewart: Journal of Physiology, 1891, vol. xii. 



4 Nouvelle mtthode anatomique pour F investigation du Syst&me nerveux, Bonn, 1851. 



5 Howell and Huber : Journal of Physiology, 1892, vol. xiiL 



