152 ANATOMICAL AND PHYSIOLOGICAL STUDIES ON 



becomes inclined inward instead of outward and subtends a 

 slight angle with the plane of the membrana basilaris. The 

 distance from the labium vestibulare to the inner edge of the 

 head of the inner pillar cell becomes smaller through the inward 

 shifting of the papilla. 



In the hair cells and the cells of the ganglion spirale we see 

 a smaller difference between the hearing and not-hearing rats. 

 Only the diameter of the nuclei of the hair cells in the hearing 

 rat diminishes a little, as it continues to do in the adult cochlea. 



All the changes just enumerated begin at the base of the 

 cochlea and progress to the apex. Therefore we see the high 

 and outward ascending papilla spiralis in turn I, while in the 

 upper turns the papilla is not yet so developed, is smaller in all 

 the constituents, and shows in general the characters of a younger 

 and less mature cochlea — conditions which disappear with age. 

 This upper and immature part seems not to respond to the test 

 for hearing. Indeed, my testing result is positive for sounds of 

 high pitch, but not for low pitch. Therefore we conclude that 

 the papilla spiralis develops functionally from base to apex and 

 that when the papilla spiralis has developed in the basal turns, 

 but not in the upper turns, it responds to sounds of high pitch 

 alone. 



Discussion 



If we assume that our tests for hearing are trustworthy, then 

 the differences between the size of the constituents of the cochlea 

 in nine-day-old rats which could and could not hear will indicate 

 what developmental changes in the cochlea of the albino rat are 

 necessary for the appearance of the hearing reflex. Whether all 

 the differences found by us are necessary is difficult to determine, 

 and the problem is open for further study; but as the matter 

 stands, our results give the closest correlation between structural 

 changes and the appearance of function which has as yet been 

 reported. 



Kreidl and Yanase ('07) studied the differences between the 

 not-hearing and hearing rat and summarized their results on 

 page 509: "Kurz vor Eintritt des Horreflexes ist das Cortische 



