QUANTITATIVE STUDIES ON MITOCHONDRIA IN NERVE-CELLS. 



39 



At first 150 fields were counted in each nucleus and the average was taken, 

 but as there was never any wide variation in the figures obtained for different 

 fields the number was limited to 50, and later to 10. Most of the averages re- 

 corded here were based on 10 field counts never on less. Lists were kept of the 

 number of mitochondria in each field as they were counted, and such variations 

 as the following were noted: In 35 fields observed in the VI nucleus the numbers 

 ranged from 20 to 26; in 10 from the mesencephalic the range was 20 to 24; in 10 

 from the VII it was 14 to 17. This uniformity ran through all the nuclei of all the 

 series, with a few exceptions that will be mentioned later. 



In order to determine the percentage error in the total, 10 fields were re- 

 counted in several cases and the error estimated, and it never amounted to more 

 than 1.3 per cent. This maximum occurred in the cells most closely crowded 

 with mitochondria; in cells having few mitochondria the recounts showed no error. 

 Table 2 contains the detailed results of specimen counts and recounts. 



TABLE 2. 



Care was taken to avoid cells whose limits could not be clearly defined. 

 Inasmuch as the cell processes and the neuroglia possess mitochondria, it was 

 necessary to choose sharply outlined cells, in order to eliminate errors due to 

 counting mitochondria outside the cell-body. 



It has been stated that the number of mitochondria in the cells of the same 

 nucleus is quite constant, but that there are some exceptions. In one animal, 

 in the VI nucleus some cells had fewer mitochondria than others, but as these 

 appeared normal in other respects they were counted, the variation ranging in this 

 instance from 13 to 21. The greater number, however, contained about 17 per 

 field. In the case of the cochlear nucleus there was a group of cells dorsal and 

 somewhat lateral to what appeared to be the main body of the nucleus. The 

 dorsal group corresponds to current descriptions of the dorsal cochlear nucleus, 

 and the larger group to the ventral cochlear nucleus. The cells of the dorsal 

 nucleus contained practically no mitochondria, were slightly smaller, and pos- 

 sessed a cytoplasm clearer than those of the ventral nucleus. Only the cells of 

 the ventral nucleus were included in the count, for it was felt that cells which 



