NEUROLOGICAL METHODS. 333 



TBZEBINSKI (Virchow's Arch., 1887, p. 1 ; ZeiLf. wise. Mil-., iv, 4, 1887, 

 p. 497) 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 

 hardening for eight days in 7 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 harden- 

 ing small pieces of brain (as suggested by GAULE, OGATA, and BECHTEEEFF) 

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

 solution, followed by alcohol. (This process produces artificial " pigment 

 spots," similar to those produced by solution of Erlicki ; they may be dis- 

 solved out by prolonged treatment with warm water, or in five minutes by 

 strong solution of LUGOL.) The tissues are of a good consistence for 

 cutting. 



Chloride of zinc has been recommended for some purposes (see 691, 

 692). 



Two recent observers, FISH (The Wilder Quarter- Century Book, 1893, 

 p. 335) and DONALDSON (Journ. ofMorphol., ix, 1894, p. 123 ; Journ. Roy. 

 Mic. Soc., 1894, p. 642), have made numerous determinations of weight and 

 volume, with the object of ascertaining what changes are produced by 

 reagents in encephala of sheep. They have found that bichromate of 

 potash produces a slight increase both of weight and volume, whereas all 

 the other reagents tried produce a diminution of both these factors. 



FLATAU (Anat. Anz., xiii, 1887, p. 323) finds that brain augments in 

 weight slightly in 10 per cent, forinol solution (spinal cord somewhat 

 more) ; whilst in 1 per cent, solution it may increase as much as 24 per 

 cent. 



685. Strengths of the Reagents. All hardening reagents 

 (except osmic acid) should at first be taken as weak as is 

 consistent with the preservation of the tissue, and be changed 

 by degrees for stronger. 



Osmic acid may be taken of 1 per cent, strength, and will 

 harden small pieces of tissue sufficiently in five to ten days 

 (EXNEB). 



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 tempera- 

 ture ; at a temperature 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. 



