324 CENTRAL NERVOUS SYSTEM. 



Probably the chloral hydrate serves to attenuate the yellow 

 colouration 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. 



667. 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 i to 1 per cent, 

 solution, according to the consistence of the brain. When 

 nominally soft he adds say -i-th to y^th per cent, of chromic acid 

 to the solution, and always -i-th to Jth 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." 



668. 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 

 colouration. After from one to three days the preparation 

 will be found to be somewhat surface-hardened ; it is taken 

 down, and the pia mater and arachnoid are removed. If the 

 pia mater does not come away completely enough the prepa- 

 ration 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 <>t iodine. The preliminary hardening may 

 now be considered complete. 



The preparation is now brought into a 3 per cent, solution 

 of bichromate of potash. (A small weight is attached to it lo 

 prevent any portion <>f it from floating above the surface of 



