40 



QUANTITATIVE STUDIES ON MITOCHONDRIA IN NERVE-CELLS. 



showed such constant and specific morphological differences could not be included 

 in the same functional category. 



Upon referring to plate 1 it will be seen that there are striking similarities 

 between nuclei of different functional categories. For example, the mesencephalic 

 nucleus (fig. 7) of the V (regarded as sensory by most authors as Johnston, 1909, 

 and Willems, reviewed by Donaldson, 1912) and the motor nucleus of the IV 

 (fig. 4) have the same number of mitochondria per unit volume of cytoplasm; 

 the visceral motor nucleus of the VII (fig. 1) and the somatic motor nucleus of 

 the XII (fig. 5) have the same average; so, too, have the vestibular of the VIII 

 (somatic sensory, fig. 2) and the motor of the III (fig. 6). Not only do nuclei of 

 different categories agree in the number of mitochondria they contain, but those 

 of the same category disagree, the numbers for the somatic motor nuclei being 

 14, 17, 20, and 22 mitochondria per unit volume of cytoplasm. Comparisons of 

 the nuclei of the same general classification are made in table 3. 



TABLE 3. 



No visceral sensory nuclei were studied. It may be seen that no distinction 

 can be made between motor and sensory nuclei on the basis of their mitochon- 

 drial content. 



In order to have some idea of the enormous number of mitochondria in the 

 cells of the nuclei of the cranial nerves and of the really tremendous variations 

 in number of mitochondria in cells of the different nuclei whose number of mito- 

 chondria per field vary only from 14.1 to 22.5, the results of some determinations 

 as to the number of mitochondria per cubic millimeter of cytoplasm will be given. 

 In nerve -cytoplasm containing 22.5 mitochondria per field, such as that of the 

 cells of the mesencephalic nucleus (fig. 7), the number of mitochondria per cubic 

 millimeter would be 284,378,159; the number for the cytoplasm of the cells of the 

 nucleus of the X nerve (fig. 8), containing 14.1 per field, would be 178,210,313. 



This study has been very carefully controlled. In the first place, several 

 observers have briefly called attention to the fact that mitochondria differ in form 

 not only in different nerve-cells, but also to some extent in the same cell. Nichol- 

 son (1916), working in this laboratory, has made a careful study of these morpho- 

 logical variations in mitochondria in the nerve-cells of the white mouse, the same 

 form which I have studied. He, however, worked with cells other than those of 



