NERVOUS SYSTEM — GENERA.T, 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 cerebrnni, and as much as 

 5 per cent, for the cerebellum. Obees'I'einer begins with 

 1 per cent., and i")rocecds 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. ifik. Techiiik., ii, p. 2'l-5) takes (for rapid 

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

 enough glycerin to make the tissues float — for a few daj'S, — 

 then pure Miiller or bichromate of potash. 



Ketz's methods [Arch. mile. Anat., 1873, 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. 



Cerehrum (Bicvan Lewis, The Human Brain, p. 10'2). — 

 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. 



