330 NORMAN CLIVE NICHOLSON 



see it in fixed and stained preparations is undoubtedly an arte- 

 fact (Mott '15, p. 68, who unfortunately extends his artefact 

 idea to the mitochondria also) , caused by the action of the fixa- 

 tive upon a material present as a diffuse deposit in living cells, 

 which fact does not, however, detract in any way from the value 

 of the numerous detailed and careful observations on Nissl 

 bodies in fixed tissues, because obviously, changes in the char- 

 acter of the coagulum (or precipitate) must be the visible mani- 

 festation of either quantitative or qualitative variations in the 

 diffuse deposit occurring in the living cell. But it is important 

 to note that the morphology of mitochondria in fixed prepa- 

 rations of nerve cells is, so far as can be ascertained, identical 

 with that seen in the living condition, which of course gives 

 additional value to observations on mitochondria. Then again 

 mitochondria are bodies quite different chemically from the 

 Nissl substance, playing in all probability an altogether different 

 role in the cell economy. 



It is clear then, that although this study of their morphology 

 will be complementary and supplementary to the older work, it 

 should enable us to push our investigations much further than 

 is possible with studies upon the Nissl substance alone. 



Comparatively little has been done thus far by other \^'orkers, 

 who have, for the most part, confined themselves to determi- 

 nations as to whether or not mitochondria do occur in adult 

 nerve cells and to the relations of mitochondria to other constitu- 

 ents of nerve cells. The only paper on the mitochondria in the 

 different, kinds of nerve cells, apart from several preliminary 

 notices of a page or more, is one by Busacca Archimede ('13, 

 p. 322) on Testudo Graeca. No precise information has been 

 gathered regarding qualitative variations in mitochondria in 

 the nerve cells of the brain of any animals above the reptiles, or 

 below them, for that matter. The following investigation- was 

 undertaken with the hope of being able to fill up this gap to a 

 certain extent by careful study of a mammal. 



