THE STRUCTURE OF CHROMOPHILE CELLS OF THE NERVOUS SYSTEM. 37 



It seems highly i)robable, therefore, that chromophile cells occur normally in the 

 brain of the white mouse and that we have to reckon with a partial solution of mito- 

 chondria just as we have for many j'ears recognized a chromatolysis, or solution of 

 the Nissl substance. 



DISCUSSION. 



This work on chromophile cells has, I believe, an important bearing upon (1) the 

 question of differential nerve-cell activity; (2) the phenomena of chondriolysis and 

 hyperchromatism; (3) the functional independence of the -mitochondria and the 

 canalicular apparatus; and (4) our conception of the structure of living nerve-cells. 



(1) The distribution of chromophile cells in the different parts of the brain is 

 interesting. The fact that they occur most abundantly in the cerebral cortex 

 and in the cerebellum, and that they are rarely foimd in the lower centers like the 

 spinal cord, would seem to indicate that the central neurones differ in some way from 

 the more peripheral ones. The difference may be one of lability, for Dolley (1914, 

 p. 56) has found that more highly specialized cells are more prone than less special- 

 ized ones to respond with structural changes to physiological experimentation. 

 Moreover, the occurrence of these cells in groups, which vary in size and in position 

 in different brains, is in accordance with our conception of the alternation of rest and 

 activity in the higher centers and may well have some bearing upon the vexed 

 problem of cortical localization, for as yet neither the mitochondria nor the canalicu- 

 lar apparatus have been considered in this connection. 



(2) We must recognize a "chondriolysis, " or a partial solution of mitochondria, 

 in nerve-cells as well as a "chromatolysis." The word "chondriolysis" was first 

 employed by Romeis (1912, p. 139) to describe the disintegration of certain mitochon- 

 dria which escaped from the cells into the uterine fluid of Ascaris. It is, to my mind, 

 more appropriate than the term "chromatolysis," which is frequently applied to the 

 so-called solution of Nissl bodies, for the simple reason that I am of the opinion 

 (1914, p. 20) that the Nissl substance is usually in solution in the living nerve-cell, 

 whereas the mitochondria are assuredly present as definite formed bodies (except 

 of course in the chromophilic condition). 



Chemical changes are undoubtedly involved in the phenomena of conduction 

 (Tashiro and Adams, 1914, p. 329) and, in view of the distinct differences in the 

 chemical constitution of the mitochondria and of the Nissl su])stancc, the one being 

 of a li])oid albumin nature (Faure-Fremiet, Mayer and Schaeffer 1910, p. 95) and 

 the other being apparently a complex nucleoprotein containing iron (Scott, 1905, 

 p. 507), it seems probable that the study of mitochondria and the changes which 

 they undergo may bring to light variations in the activity of the nerve-cell which 

 could never be detected by the study of the Nissl substance alone. Quite ai)art 

 from the role of the nucleus in the elaboration of the Nissl substance and the purely 

 cytoplasmic nature of mitochondria, there is further evidence of a functional diver- 

 sity between the two structures. I have found that in the nerve-cells of the mouse 

 the mitochondria vary directly with the volume of the cytoplasm and that the Nissl 

 substance varies inversely with the nucleus cytoplasmic ratio; also that the mito- 

 chondria are of more general occurrence in nerve-cells than the Nissl substance. 



