GROWTH OF THE INNER EAR OF ALBINO RAT 



125 



For the measurement of the nerve cells a Zeiss system was used 

 with a micrometer eyepiece, having each division equal to 2\l. 

 Since we have in the radial vertical section of the cochlea of the 

 rat at least four turns, there are four cell groups available in 

 each section (fig. 3). The ten largest cells in each ganglion 

 were measured, and thus a total of forty cells in a section were 

 taken for the measurement of the nucleus and the cell. 



We used, as stated, four cochleas in each age group, so that 

 160 cells were measured for each age. Also in the cross-sections 

 the four nearly corresponding turns were used for the measure- 

 ments, selecting the ten largest cells in each turn. 



In the measurement of the cell bodies the two maximum 

 diameters at right angles to each other were determined, and 

 also the two corresponding diameters for the nuclei. 



Here it is to be noted that the expressions turn I, II, III, 

 and IV are used in the same sense as in the earlier chapters. 



In table 95 (chart 40) are given the values for the average 

 diameters of the cell bodies and their nuclei in the ganglion 

 spirale in the radial vertical section according to fourteen age 

 groups. Under 'cell body, diameter,' the first column gives the 

 long, the second the short, and the third the computed diameter; 

 i.e., the square root of their products. These last values ap- 

 proximate the mean diameters of the nerve cells. At the foot 

 of the third column are given the ratios from 1 to 20, 1 to 546, 

 and 20 to 546 days. The values for the diameters of the nuclei 

 are similarly given and also the ratios. 



