GROWTH OF THE INNER EAR OF ALBINO RAT 7 



The bony labyrinth with its surrounding bones was then 

 placed in the fixing solution for two weeks, the fluid being re- 

 newed every day. 



The fixing solution which I used consists, according to Yoshii 

 ('09), of— 



10 per cent formol , 74 parts 



Muiler's fluid.. 24 parts 



Glacial acetic acid. . 2 parts 



According to Tadokoro and Watanabe ('20), this solution 

 is one of the best, ranking with that of Wittmaack ( '04, '06) and 

 that of Nakamura ('14). 



This injection method is sometimes difficult to apply to very 

 young rats on account of the small size and the delicacy of the 

 vessels. When injection failed in very young animals, then 

 immediately the head was cut off and put directly in the fixing 

 fluid. Owing to the incomplete calcification of the very young 

 cochlea, the fixing solution enters rapidly and fixes the deep- 

 seated organs in good condition. Since the parts of the internal 

 ear are not yet well developed in the very young rats, they do 

 not suffer from this method of fixation as do the older cochleas. 



Indeed, no differences are to be seen between the sections 

 prepared by vital fixation and by decapitation in very young rats. 



For decalcification I have employed the following solution 

 during three days, renewing it every day. 



Decalcifying fluid 



5 per cent aqueous nitric acid 49 parts 



10 per cent formol 49 parts 



Glacial acetic acid 2 parts 



After the specimens had been washed in running water for 

 three days, they were passed through the alcohols from 50 to 97 

 per cent. For the imbedding I have used 'parlodion' with good 

 results. Here it is to be mentioned that all the cochleas were 

 treated in the same way, even unossified cochlea being passed 

 through the decalcifying fluid, so that there should be absolutely 

 no differences in treatment. 



