92 Neurological Technique 



the specimen when it does sink, but any effort to hold it sub- 

 merged should be avoided, lest such effort result in a distortion 

 of its normal shape. 



2. After 48 hours in the zinc chloride solution, the brain will 

 become sufficiently hardened for the pia mater to be removed. 

 To do this use blunt-pointed dissecting forceps and proceed 

 carefully, avoiding injury to the surface of the gyri. 



3. The pia removed, put the brain back into the zinc chloride 

 solution for 3 or 4 days more, or for about i day after it has 

 sunk to the bottom of the vessel. 



4. To complete the hardening and to dehydrate, transfer 

 directly to I or 2 volumes of commercial alcohol for 2 or 3 

 weeks, change the alcohol after the first and third days, and two 

 or three times during the rest of the period. Keep the vessel 

 closed. 



The bottom of the vessel should be padded with absorbent 

 cotton, and the brain should be turned repeatedly during the first 

 3 or 4 days to prevent any malformation which may result from 

 pressure upon the bottom of the vessel. 



The specimen will shrink somewhat in the alcohol, but this 

 can hardly be avoided. 



5. Replace the alcohol with enough oil of turpentine to cover 

 the brain, and let remain for 2-4 weeks. 



The more complete the dehydration by the alcohol, the 

 better will be the penetration of the oil of turpentine. 



The oil of turpentine should be changed two or three times 

 during the first two weeks, and the vessel should be kept closed. 



In the oil of turpentine the brain assumes a semi-translucent, 

 brownish appearance. 



6. Transfer from the turpentine to a vessel in a thermostat 

 containing enough melted "soft" paraffin to cover the specimen, 

 for 4-6 days. 



The paraffin should melt at about 40" C, and the thermostat 

 should be kept at a temperature but a few degrees above the 

 melting point of the paraffin, lest further shrinkage result. 



7. After the brain has become well infiltrated with the 



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