340 NORMAN CLIVE NICHOLSON 



are in all likelihood associated, in some obscure way, with 

 changes in their environment; that is, in the cytoplasm. The 

 intimate bearing of such differences in the cytoplasm upon the 

 doctrine of neurone specificity is apparent, inasmuch as any dif- 

 ference in the specialized activity of a cell, like conduction, is in 

 all probability related to some difference in the cytoplasm rather 

 than in the nucleus. This is not at variance with the results 

 which others have obtained. 



Since Cowdry ('14, p. 21) has found that there is a surprising 

 constancy in the mitochondria in the spinal ganglion cells of 

 different vertebrates, including man, it is altogether likely that 

 the variations in morphology which I have described in the 

 mitochondria in different types of cells in the brain of the white 

 mouse may hold in other mammals also. This seems to indicate 

 that when differences in the morphology of the mitochondria 

 occur they are not chance variations but are fundamental 

 differences ingrained in the very organization of the cell. 



Moreover Thurlow ('16, p. 253) has found, by a detailed quan- 

 titative study of mitochondria in the cells of the different cranial 

 nerves, that the actual number of mitochondria per unit vol- 

 ume of cytoplasm varies considerably. The largest amount of 

 mitochondria was found by her in the cells of the mesencephalic 

 nucleus of the trigeminal nerve and the least in the visceral 

 motor nucleus of the seventh. Even if we adopt the ultraconser- 

 vative view that the mitochondria are purely deutoplastic ele- 

 ments and do not play an active role in cellular physiology 

 (which I would be loath to do) it is perfectly obvious that their 

 presence in great amount in some cells and in very small numbers 

 in others, must indicate either a qualitative or else merely a 

 quantitative difference in the nature of the activity of the cells 

 in question. For it is impossible to regard the activity of a cell 

 as being entirely uninfluenced by the heaping up in it of inert 

 substances. 



Pathological hearing. The practical value of this work lies in 

 its possible pathological application. The standardization of 

 material for experiment, the enumeration of the qualitative 

 variations which normally occur in mitochondria in the differ- 



