GROWTH OF THE INNER EAR OF ALBINO RAT 



141 



I have calculated the cylindrical surface of the hair cells 

 according to the formula for the lateral surface of a cylinder; 

 therefore, this area equals 2 % r a (r = radius, a = height of the 

 cylinder) . As the hair cells are more or less pointed at their lower 

 end, the surface obtained by this formula has nearly the value of 

 the total surface of the hair cells less that for the upper end disk. 



As has been already shown, both classes of cells grow rapidly 

 from birth to twenty days, and after that both tend to decrease 

 slightly in volume. It is evident that during the growing period, 



TABLE 110 



Comparison of the ratios of the volume of the cells of the ganglion spirale with the 

 ratios of the areas of the cross-section of the inner and outer hair cells 



of the organ of Corti 



from one day to the end of the record, the volumes of the ganglion 

 cells increase more rapidly than do the cylindrical areas of the 

 hair cells (table 108). If we seek a numerical expression of these 

 relations, it seems best to start not with the values at birth, but 

 with those at nine days of age when the cochlea is just beginning 

 to function, and to extend the comparison only up to twenty clays 

 when both groups of cells have reached their maximum size. 

 Thus at nine days (table 108) the volume of the ganglion cells 

 is 1317 [i 3 , while at twenty days it is 3105 ^ 3 , or as 1 : 2.3, while 

 the area of the cylindrical surfaces of the hair cells at the respective 



