NIfiRVOUS SYSTEM — GENERAL METHODS. 381 



743. Other Reagents. — Osmic acid is hardly useful for specimens 

 of more than 2 or 3 millimetres' thickness. These, at a sti-ength of 1 

 per cent., it will harden well in five to ten days. 



Chromic acid is not much used alone. Its action is rapid, but uneven, 

 and causes shrinkage and brittleness. A very little (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 sti-engths of 10 to 12 

 per cent., and gives particularly tough preparations. 



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

 preservation of ganglion cells, according to Anna Koxlaeewski (see 

 Zeit. iviss. Mih., iv, 1887, p. 387). 



TllZEBlNSKi (Virchow's Arch., 1887, p. 1 ; Zeit. wiss. Mih., iv, 1887j 

 p. 497) finds that ganglion cells (of the spinal cord of the rabbit and 

 dog) are best preserved by hardening for eight days in 7 per cent, 

 solution of corrosive suhlimate, followed by alcohol containing 0'5 per 

 cent, of iodine. Similarly, Diomidoff {ibid., p. 499), with brain. This 

 process produces artificial " pigment spots " ; they may be dissolved out 

 by prolonged treatment with warm water, or in five minutes by strong 

 solution of LuGOL. 



TlSH [The Wilder Quarter-Century Booh, 1893, p. 335) and Donald- 

 son [Journ. o/ Jlfor^TioZ., ix, 1894, p. 123) have found that bichromate of 

 potash produces a slight increase both in weight and volume of brains 

 of sheep, whereas all the other reagents tried produce a diminution of 

 both these factors. 



Several observers have lately been using acetic alcohol. So Timofbew, 

 Intern. Monatsschr. Anat. u. Phiju., xv, 1898, p. 259 (Caknoy's second 

 formula, § 85). 



Mann (Methods, etc., p. 95), for cell-studies, puts for twenty-four 

 hours into solution of 5 parts of iodide of potassium and 25 of iodine in 

 100 of water, then into 70 per cent, alcohol. 



Fish {The Wilder Qaarter-Ceutury Booh, 1893, p. 393) takes 

 Water . . .400 c.c. 



95 per cent, alcohol . 400 „ 



Glycerin . . 250 „ 



Zinc chloride 20 grms. 



Sodium chloride 20 grms. 



for about three days, then transfers for a week or more to a mixture 

 of equal part.s of the fluid and 70 per cent, alcohol, and finally stores in 

 90 per cent, alcohol. 



Ohlmachbb, recommends his sublimate mixture, § 05, Kodis {Arch, 

 mile. Anat., lix, 1901, p. 212) fixes in saturated solution of cynuide of 

 mercury, brings into 10 per cent, foi-mol, and sections by the freezing 

 method. 



Kelis {Ball. Acad. Sc. Belg., 1899, 1900, p. 72*3) fixes spinal ganijUa for 

 twenty-four hours in a solution of 20 grms. sulphate of copper, and sub- 

 limate to saturation, in a litre of 7 per cent, formol with 5 c.c. of acetic 

 acid. 



King {Anat. Uec, iv, 1910, p. 213) after trying over twenty-five 



