390 CENTEAL NERVOUS SYSTEM. 



to the interior, they may be at once removed to the following: 

 mixture : 



Bichromate of ammonia . . 1 grm., 



Water . . . 400 c.c., 



in which they remain for one week. Then change the solu- 

 tion to one of 1 per cent, for one week ; and let this be followed 

 by a solution of 2 per cent, for another week, or longer if 

 required. The pieces will now be sufficiently hard for cutting ; 

 they may be kept permanently in solution of chloral hydrate, 

 twelve grains to the ounce. 



Probably the chloral hydrate serves to attenuate the yellow 

 coloration produced by the chromic liquids. 



This is a process particularly adapted to the preparation of 

 large segments of brain. The consistence is very tough and 

 firm. 



738. Entire Encephalon (DEECKE, Journ. Roy. Mic. Soc., 1883, 

 p. 449). "To harden the entire brain so that the inside and 

 the outside shall be hardened equally and properly, Dr. Deecke 

 finally adopted bichromate of ammonia in | to 1 per cent, 

 solution, according to the consistence of the brain. When 

 nominally soft he adds say | to T V per cent, of chromic 

 acid to the solution, and always -J to { of the whole volume 

 of alcohol. It is then placed in a refrigerator and the fluid 

 changed frequently. After a month add a little more alcohol 

 from week to week until the alcohol is 90 per cent. This is 

 changed as often as it is discoloured. The treatment requires 

 from twelve to eighteen months." 



739. BETZ'S Methods (Arch. f. mik. Anat., 1873, p. 101). The spinal 

 cord, medulla oblongata, and pons Varolii are treated as follows : The 

 dura mater is removed, and they are hung up in a cylinder containing 75 to 

 80 per cent, alcohol, to which is added enough iodine to produce a light 

 brown coloration. After from one to three days the preparation will be 

 found to be somewhat surf ace -hardened ; it is taken down, and the pia 

 mater and arachnoid are removed. If the pia mater does not come away 

 completely enough the preparation is put back for some days into the 

 alcoholic iodine. The membranes having been removed, the preparation 

 is put back into the original fluid, which is found to have become colourless 

 owing to absorption of the iodine by the tissues. Fresh quantities of a 

 strong solution of iodine in alcohol are from time to time added to the 

 liquid in order to keep it at its original strength of iodine (as shown by the 

 colour). If the membranes have been carefully removed it will be found 

 that after about six days the preparation ceases to take up further quantities 

 of iodine. The preliminary hardening may now be considered complete. 



