334 NORMAN CLIVE NICHOLSON 



almost beyond the limits of accurate measurement. Compara- 

 tively large areas of cytoplasm seem to be devoid of mitochon- 

 dria. An abrupt change occurs in the form of mitochondria as 

 we pass to the neighboring cells of the pontile nucleus, in which 

 the block-like mitochondria, as well as the peculiar synapses, 

 are absent. 



It has been generally assumed (Busacca Archimede '13) that 

 the mitochondria occur between the Nissl bodies and not within 

 them. So far as I have been able to ascertain, with a method 

 of staining which permits of observation of Nissl substance and 

 mitochondria at the same time, this is not the case. Indeed one 

 would not expect to find the mitochondria between the Nissl 

 bodies in view of the fact which "Cowdry ('14, p. 20) emphasizes, 

 that the Nissl substance is present as a homogeneous diffuse 

 deJDosit in the living cell and that the Nissl bodies as seen in the 

 fixed preparations are produced by a process of coagulation or 

 precipitation. 



It may be mentioned in passing that cells with the typically 

 filamentous variety of mitochondria (reticular formation cells, 

 fig. 11), the granular or rod-like mitochondria (mesencephalic 

 cells, fig. 5) and the blocklike mitochondria (cells of trapezoid 

 nucleus, fig. 2) all occur in the same section, proving that the 

 differences in form of mitochondria cannot be due to variations 

 in technique. Furthermore the variations in morphology were 

 found to occur constantly in all members of the species which 

 were examined. 



Another fact worthy of note is that cells of quite different type 

 like the mitral cells of the olfactory bulb (fig. 3), the Purkinje 

 cells of the cerebellum (fig. 9), and the cells of the septum (fig. 

 10) all contain mitochondria of the same kind. It is clear that 

 variations in the form of mitochondria cannot be used to dif- 

 ferentiate between sensory and motor cells, nor can quantita- 

 tive variations be so used, according to Thurlow ('16, p. 253). 

 This is in marked contrast to variations in the Nissl substance, 

 which can be used for such differentiation (Malone '13, p. 129). 

 Again, the general assumption that the morphology of the 

 mitochondria is related to the shape of the cell containing them 



