278 PRACTICAL HISTOLOGY. 



including the tympanic membrane, and the other 

 the cochlea are separated from one another, and the 

 membrane part may at once be dropped into weak 

 spirit and put aside to be subsequently stained and 

 mounted. From the other part as much as possible 

 of the substance of the petrous bone is snipped away, 

 bit by bit, from around the base of the cochlea with 

 scissors or bone forceps, but great care should be 

 taken in approaching the cochlea itself, as this is 

 very readily split. When the surrounding bone has 

 been in this way removed, the cochleas are dropped 

 into Miiller's fluid. In this they are to be left for a 

 week or fortnight even a longer immersion will do 

 them no harm until the sort structures in the in- 

 terior are somewhat hardened. The process is then 

 completed, whilst the bone is at the same time 

 softened by transferring the cochleae to a saturated 

 solution of picric acid. When the bone is com- 

 pletely softened, a process which is much facilitated 

 by frequent disturbance of the fluid, the cochleas are 

 transferred to weak spirit (half water), and in 

 twenty-four hours more to strong spirit. After 

 beini>; in this for two or three days they are ready for 

 embedding. The best mass to use for this purpose 

 is a mixture of wax and cacao butter, equal parts of 

 each. One of the prepared cochleas is fixed by a pin 

 in the embedding box in such a position that the 

 plane in which the sections are made shall be exactly 

 parallel with the axis of the cone which the cochlea 

 forms, and the cacao-butter and wax, previously 

 melted and thoroughly mixed, are poured into the 

 mould. When the mass has become hard, sections 

 may be made ; the first ones will include only the 

 large basal turn of the cochlea, then the higher turns 

 will all be included in succession, until at last the 

 modiolus is reached. All the sections which have 

 been made up to this point may be rejected. Great 

 care must now be taken to make thin and complete 

 sections of this central part. They will of course be 

 triangular in shape, with a rounded apex; the sec- 



