SPINAL CORD. 321 



harden small pieces of tissue sufficiently in 5 to 10 days 



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. Obersteiner begins with 1 per 

 cent, and proceeds gradually during six to eight weeks to 2 

 or 3 per cent. (This is at the normal temperature ; at a tem- 

 perature of 35 to 45 C. the hardening can be got through 

 in one or two weeks). 



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. 



Chromic acid is not much used alone. See supra, 70. It forms part of 

 some of the mixtures mentioned below. A very little chromic acid (say one 

 to two drops of 1 per cent, solution for each ounce) added to bichromate 

 solution will do no harm, and will quicken the hardening. 



Nitric acid has been and still is employed in strengths of 10 to 12 per 

 cent., and gives particularly tough preparations. Perhaps a weaker solution 

 might give good results, but I cannot find that any such have been tried. 



Neutral acetate of lead in 10 per cent, solution affords an excellent pre- 

 servation of ganglion-cells, according to ANNA KOTLABEWSKI (see Zeit. f. 

 wiss. Mik., iv, 3, 1887, p. 387). 



TBZEBINSKI (Virchow's Arch., 1887, p. 1 ; Zeit.f. wiss. Mik., iv,4, 1887, 

 p. 11)7) finds that as regards the faithful preservation of ganglion-cells (of 

 the spinal cord of the rabbit and dog) the best results are obtained by har- 

 dening for eight days in 10 per cent, solution of corrosive sublimate, followed 

 by hardening in alcohol containing 0'5 per cent, of iodine. 



DIOMIDOFF (ibid. p. 499) also obtained very excellent results by har- 

 dening small pieces of brain (as suggested by GAULE, OGATA, and BECHTEBEFF) 

 for from five to nine days (not more in any case) in 7 per cent, sublimate 

 solution, and then putting the tissues for twenty-four hours into 50 per 

 cent, alcohol, and for the same time into 70 per cent, and 96 per cent, alcohol 

 successively. (This process produces artificial " pigment spots " similar to 

 those produced by solution of Erlicki ; they may be dissolved out by pro- 

 longed treatment with warm water, or in five minutes by strong solution 

 of LUQOL.) The tissues are of a good consistence for cutting. Chloride 

 of zinc has been recommended for some purposes, see below, 673. 



The next following paragraphs give in detail some methods of hardening 

 recommended l>y some of the most competent workers. 



662. Spinal Cord (KKAUSK, Arch.J. mik. Anat., 1875, p. 226). 

 Solution of Muller, twenty-four hours. Then chromic acid, 

 1 per cent. On the fourth day the solution must be changed 



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