6 * ANATOMICAL AND PHYSIOLOGICAL STUDIES ON 



MATERIAL 



For the present studies forty male and thirty female albino 

 rats were used, representing every phase of postnatal growth and 

 having approximately standard body weights. These were all 

 from the colony of The Wistar Institute, and were sometimes 

 from the same, and sometimes from different litters. 



At first all these rats were tested for their ability to hear 

 and their equilibrium, and it was ascertained that after about 

 twelve days of age, or somewhat earlier, they responded posi- 

 tively to the test for hearing. Such examinations were deemed 

 necessary, to make certain that the rats used were normal. 



I have arranged the animals thus tested in fourteen groups 

 according to age, each group having five individuals in it. Serial 

 sections from all these cochleas were made by methods to be 

 given later. Most of them were in the plane of the vertical 

 axis of the cochlea, but some were at right angles to it. 



From the former I selected four ears in each group for the 

 study of the growth of the cochlea. For the study of the growth 

 of the ganglion vestibulare, I have used for the most part the 

 same specimens. For the study of the sections at right angles 

 to the vertical axis of the cochlea, sections from one ear of each 

 group were used. 



TECHNIQUE 



In order to obtain good preparations of this delicate organ, 

 the method of vital fixation (injection under anaesthesia) was 

 used. The method employed, and which proved almost ideal, 

 was that introduced by Metzner and Yoshii ('09), Siebenmann 

 and Yoshii ('08) and somewhat improved by Sato ('17). After 

 the animals had been tested to make sure that they were quite 

 normal, the fixing solution was injected through the aorta under 

 ether. The brain was then carefully removed, care being taken 

 not to drag the trunk of the nervus acusticus, as noted by Nager 

 ('05), and the bulla tympanica was opened to allow the further 

 penetration of the fluid. 



