GROWTH OF THE INNER EAR OF ALBINO RAT 147 



responded to the test very evidently at noon on the ninth day, 

 but the others did not. The sound which was effective was 

 fairly intense, but to a faint and low-pitched sound this rat 

 did not respond. In this case the external auditory canal was 

 open. In the others there was in some a small open canal, 

 but more or less closed by a cellular plug. In the latter cases 

 I removed this obstruction without much difficulty or damage 

 by washing, yet no reaction could be obtained to the stimuli. 

 As it was to be expected, that also in the latter the reflexes would 

 very shortly appear, all the cochleas of these young rats, both 

 the not-hearing and hearing, were fixed by the method pre- 

 viously described and later examined. 



In chapter 1, in which I followed the growth changes in the 

 constituents of the membranous cochlea and in its ganglion 

 cells from birth to maturity, including ' not hearing ' and ' hearing ' 

 rats, very evident differences were observed in rats between 

 nine and twelve days of age. In view of this, it will be of in- 

 terest to compare the measurements obtained from the 'not 

 hearing' and 'hearing' rats nine days old and members of the 

 same litter. From the differences thus obtained we can conclude 

 concerning the developmental changes in the cochlea requisite 

 for the first appearance of hearing, provided there are no obstacles 

 in the sound-conducting apparatus or deficiencies in the central 

 organ. 



In table 113 are given the values for the size of the several 

 constituents of the cochlea from a rat which did not hear and 

 one which did, at nine days. The former data are the averages 

 from four cochleas, while the latter are from two. The table 

 shows in a striking way that where there is a significant differ- 

 ence. The values obtained from the rat which could hear are 

 usually larger than those of the rat which could not hear. 



Among these measurements we see sometimes very marked 

 and sometimes only slight differences. Only the radial distance 

 between the labium vestibulare and the inner edge of the head 

 of the inner pillar cell in the first two turns and the diameter of 

 the nuclei of the inner and outer hair cells are in the former smaller 

 than in the latter. In both instances, however, these smaller 



