6 PRACTICAL HISTOLOGY. 



be not tough and leathery at the end of six weeks, place it 

 in - per cent chromic acid for a fortnight, and then in rec- 

 tified spirit. If the brain be placed in a too strong chromic 

 acid solution, or if it be too long exposed to the action of 

 even a moderately strong solution, it becomes friable and 

 useless. Procure a portion of human cerebrum (parietal 

 lobe), as fresh as possible, and treat it in the same manner 

 as the cat's brain. A portion of human cerebellum may 

 be prepared in the same manner. At the end of six or 

 seven weeks transfer all the tissues to rectified spirit to com- 

 plete the hardening. The brain and spinal cord should 

 always be placed on cotton wool in their hardening fluid, 

 in order that the fluid may reach every part equally. 



15. Remove the muscles, but not the periosteum, from 

 the bones of the upper or lower limb, and remove both from 

 the lower jaw. Divide the jaw and the long bones trans- 

 versely in two or three places, and put them into the 

 chromic and nitric fluid (Solution 5). Change the fluid re- 

 peatedly until the bone is just sufficiently softened, and then 

 transfer it to rectified spirit. If the softening is not com- 

 pleted in a month, double the quantity of nitric acid in the 

 fluid, or place them simply in dilute nitric acid (2 per cent). 

 The softening is most rapidly accomplished by suspending 

 the bones in the fluid. For this purpose they may be 

 placed in a muslin bag. The bone must not, however, 

 remain in the softening fluid after all calcareous matter has 

 been removed. 



16. Place a piece of human scalp, skin from palmar 

 surface of finger, in chromic and spirit fluid (Solu- 

 tion 3). Change the fluid at the end of eighteen hours. 

 At the end of a month transfer to rectified spirit. 



17. Remove the petrous portion of the temporal bone, 

 open the tympanum, pull the stapes from the oval fene- 

 stra, and place the cochlea in chromic and spirit fluid. 

 Change it at the end of eighteen hours, and again on the 

 sixth or seventh day. But if a copious brown precipi- 

 tate fall, change the fluid every third day. On the tenth 

 or twelfth day transfer to chromic and nitric fluid. Change 

 the fluid frequently until the bone is soft. Then place 



