PROPORTIONS OF THE TECTORIAL MEMBRANE 15 



decalcifying first, it is always the thicker bony regions which 

 give trouble with the sectioning knife. 



An additional advantage of the bichromate-formalin-acetic 

 mixture is that specimens fixed in it do not require a period of 

 washing with w^ater preliminary to dehydration for embedding. 

 All the drawings given here were made intentionally from sec- 

 tions of cochleae fixed in this fluid. 



Dehydration required especial care. Tectorial membranes 

 fixed without distortion are often badlj^ disfigured by the treat- 

 ment preparatory to embedding. Here no grade of alcohol of 

 more than 10 per cent greater strength than the preceding was 

 used. Further, it was found best to make up the desired grades 

 of alcohol and let each stand before using long enough for all 

 the fine bubbles of air resulting from the mixture with water 

 to pass off. Otherwise these bubbles will collect upon and pos- 

 sibly form within the cochleae. The specimens were transferred 

 direct from the fixing fluid to 20 per cent alcohol. Then, allow- 

 ing them to remain in each grade from 3 to 12 hours according 

 to convenience, they were subjected in succession to 30, 40, 

 50, 60, 70, 80, 90, 95 per cent and absolute alcohol. All clear- 

 ing agents preparatory to embedding in paraffin, especially 

 xylol, were found especially injurious except with the very 

 youngest stages studied. The absolute alcohol was in all cases 

 allowed to act at least 6 hours and then replaced by ether-alcohol 

 and the specimens embedded in celloidin in the usual way. 



The celloidin blocks were hardened with chloroform (not with 

 water) and, to obtain transparency of the celloidin, the blocks 

 were first placed in 95 per cent alcohol for an hour or so before 

 the 80 or 70 per cent alcohol in which they were sectioned. Some 

 of the blocks were transferred from the chloroform to cedar oil 

 in which they remained long enough to become cleared, and then 

 sectioned with the knife flooded with cedar oil. The latter 

 procedure, though excellent for orientation, because of the trans- 

 parency of the blocks, and for ease in sectioning, requires more 

 time before and after sectioning than sectioning in alcohol and 

 it did not seem to give any better results. 



