THE PHYSIOLOGICAL CHEMISTRY OF THE NEURON. 561 



the following main facts connected with nerve-degeneration 

 seem to us to find a ready explanation: 



Section of a motor nerve will cause degeneration of the pe- 

 ripheral fragment, and atrophy of the muscles supplied by it. 

 We have emphasized the functional importance of a continuous 

 supply of nervous energy, both upon the vascular and cellular 

 elements of any organ. 



There is no degeneration of the upper, or proximal, frag- 

 ment, however, except as far as the first Ranvier node. This 

 has been ascribed to traumatism, but we can readily understand 

 now that section through an internodal segment destroys the 

 mechanism of that segment, the supply of oxidizing substance 

 failing to reach the myelin through the fibrils and their 

 canaliculi. Its nutritional or "passive" function is thus ar- 

 rested. 



That the nerve and even its neuron require some of their 

 own energy to permanently sustain their own life, as empha- 

 sized by Marinesco, 49 especially when long stretches of nerve are 

 involved, is shown by the fact that if the seat of its ultimate 

 distribution is destroyed, a muscle, for instance, or if it is 

 disconnected from the latter, the nerve may, as sometimes 

 occurs after amputations and peripheral neuritis, degenerate, 

 and the process extend up to and include the cornual cell. 

 That this does not always occur is doubtless due to the fact 

 that the subdivisions of a nerve all contribute to the main- 

 tenance of its life, and that the chances that degeneration of 

 a long nerve will occur are proportionate to the number of 

 branches it supplies in its course. 



The sensory nerves show the same attributes, but, of 

 course, in a reversed direction. Section of the posterior root 

 above a ganglion is followed by degeneration of the dorsal 

 stump, which may include the extension into the cord. Am- 

 putation sometimes causes not only atrophy of the peripheral 

 fibers, but also of the ganglion-cells and their prolongations 

 in the columns. "The living muscle seems so organized that 

 without nervous stimulation it can no more live than can the 

 tropical animal without warmth or the rose without water," 



* Marinesco: Neurol. Centralbl., Bd. xi, 1892. 



