134 Modern Microscopy 



■watery solution of chromic acid, and for every ounce add 5 

 drops of nitric acid. This fluid will soften the femur of a 

 dog in about three weeks ; larger bones will take longer. 

 Change the fluid several times, and test its action by 

 running a needle through the thickest part of the bone. If 

 it goes through easily, the bone is soft enough ; if not, 

 continue the softening process a little longer. When soft 

 enough transfer to water, and soak for an hour or two ; 

 then pour off the water and add a 10 per cent, solution of 

 bicarbonate of soda, and soak for twelve hours to remove 

 all trace of acid. Wash again in water, and place in 

 methylated spirit until required. Bones and teeth should 

 always be softened in a large quantity of the decalcifying 

 solution. 



Olfactory Region. — Divide with a saw the head of a 

 freshly killed rabit or guinea-pig longitudinally, and 

 parallel with the nasal septum. Cut out the septum so as 

 to expose the olfactory region, which is recognised by its 

 brown colour. Dissect out a portion including some of the 

 turbinated bones. Harden this in Miiller's fluid for three 

 or four days. Then transfer to chromic and nitric acid 

 decalcifying solution, and soak until the bones are quite 

 soft. Wash well in water to remove all trace of acid, and 

 complete the hardening in methylated spirit. 



Cochlea. — Dissect out the internal ear of a freshly killed 

 young guinea-pig, open bulla with bone-forceps, when a 

 conical elevation, the cochlea, will be seen. Eemove as 

 much of the surrounding bone as possible, and place the 

 cochlea in Miiller's fluid for two weeks to harden the delicate 

 nervous tissues. Then transfer to chromic and nitric acid 

 decalcifying solution, and soak until the bone is soft. Place 

 in weak spirit for a day or two, and then transfer to strong 

 methylated spirit. 



Corrosive Sublimate. — Tissues may be fixed very quickly 

 in corrosive sublimate. Make a saturated solution in 5 

 per cent, glacial acetic acid. The specimens should be 

 removed from the solution as soon as they are fixed, 



