332 NORMAN CLIVE NICHOLSON 



tion in the morphology of mitochondria occmTing in the same 

 type of cells, in a single center, which actually possess similar 

 mitochondria. In fact one comes to suspect those preparations 

 which exhibit a great dimorphism of mitochondria in cells of the 

 same type. Poor penetration of the fixative generally results 

 in the filamentous mitochondria breaking up into granules, or 

 else forming spherules; a phenomenon well known in other 

 tissues. There is no evidence that filaments are ever formed as 

 a result of bad technique. In all my observations a careful 

 check has been kept upon the technique. 



In some nerve cells, like the anterior horn cells of the spinal 

 cord (fig. 1), and the large cells of the reticular formation of the 

 midbrain (fig. II), the mitochondria are present in the form of 

 filaments of variable length, which frequently attain a length of 

 4.66 microns in the former and 6.49 microns in the latter. They 

 are much longer in the processes than they are in the cell body. 

 They are more granular in the immediate vicinity of the nucleus 

 where they are also more numerous. This is a striking feature 

 of all the cells observed. It is well to remember at this point 

 that filamentous mitochondria occur in other types of cells also; 

 indeed, filamentous mitochondria occur more frequently than 

 any other form in the central nervous system. 



Again we find cells with mitochondria in the form of granules 

 or short plump rods. The cells of the mesencephalic nucleus of 

 the trigeminal nerve (fig. 5) are crowded with mitochondria of 

 this description. The granules are about 0.29 microns in di- 

 ameter and the filaments about 0.62 microns long. Mitochon- 

 dria of intermediate size and shape are invariably to be seen. 

 It is interesting to note that the same sort of mitochondria are 

 encountered in the large cells of the Gasserian gangUon, because 

 the nature of these mesencephalic cells has been long in dispute 

 and this new point of similarity between them and cells known 

 to be sensory constitutes additional evidence that they themselves 

 are sensory, and as Thurlow^ also has emphasized, supports the 

 view that they are in reality neural crest cells which have been 

 enclosed in the neural tube in the course of development. This 



1 Thurlow, personal communication. 



