NERVOUS SYSTEM GENERAL METHODS. 379 



In view of the slowness of penetration of chromic salts, it 

 is often advisable to treat preparations for twenty-four hours 

 or more with alcohol of 80 to 90 per cent., or formol, before 

 putting them into the hardening liquid, or to add formol 

 (say 3 per cent.) to it, in order to avoid maceration of the 

 deeper layers of tissue. 



Bichromate of potash should be taken at first of not more 

 than 2 per cent, strength ; this is then gradually raised to 

 3 or 4 per cent, for the cord and cerebrum, and as much as 

 5 per cent, for the cerebellum. OBERSTETNER begins with 

 1 per cent., and proceeds gradually during six to eight 

 weeks to 2 or 3 per cent. (This is at the normal tempera- 

 ture ; at a temperature of 35 to 45 C. one or two weeks 

 will do.) 



Bichromate of ammonia should be taken of half the 

 strength recommended for bichromate of potash, or even 

 weaker at first ; it may be raised to as much as 5 per cent, 

 for cerebellum towards the end of the hardening. 



NISSL (Encycl. Mils. Technik., ii, p. 245) takes (for rapid 

 hardening) 100 parts of liquid of Muller, 3 of formol, and 

 enough glycerin to make the tissues float for a few days, 

 then pure Muller or bichromate of potash. 



BETZ'S methods (Arch. mile. Anat,., J873, p. 101). Brain 

 and spinal cord are first hardened, for some days or weeks, 

 in 70 to 80 per cent, alcohol containing enough tincture of 

 iodine to give it a light brown coloration. (As fast as the 

 alcohol becomes colourless more iodine must be added.) 

 Then definitely hardened in bichromate of potash, of 3 per 

 cent, for spinal cord, medulla oblongata, and pons, 5 per cent, 

 for cerebellum, and 4 per cent, for cerebrum. 



Unduly neglected nowadays. 



Cerehrtim (BuvAN LEWIS, The Human Brain., p. 102). 

 Methylated spirit, twenty- four hours in a cool place. Miiller's 

 solution, three days in a cool place. Then change the liquid ; 

 and after three days more substitute a 2 per cent, solution 

 of potassium bichromate. At the end of the second week a 

 solution of double the strength may be added ; and if at the 

 termination of the third week the mass is still pliable, and 

 of the consistence of ordinary rubber, it is as yet unfit for 

 section-cutting, and the reagent should be replaced by a 

 solution of chromic acid. 



