NERVOUS SYSTEM — GENERAL METHODS. 377 



the chromic salts, and even than alcohol, and allows of the 

 most various utains, including silver neuro-fibril stains and 

 the Golgi impregnation. 



Several writers insist that for nervous tissue it should not 

 be acid; but some prefer it acid (see "Retina"). For 

 neuro-fibrils it certainly should be neutral. To neutralise, 

 it is generally sufficient to make up the solutions with taj)- 

 ivater. It is not likely to orerharden. 



I use 1 part of formol to 9 of water (or 8 if the formol 

 has been keep long). 



Weigebt {Beit. Kenidn. norm, mensch. Neuroglia, 1895, 

 p. 1146) puts portions of material of not more than half a 

 centimetre in thickness for four days into a " 4 per cent, 

 solution of formol" (meaning, presumably, 4 per cent. 

 formaldehyde). 



Marcus (quoted from Fish, see below) hardens spinal cord 

 for two or four weeks in a ^ per cent, solution of "formalin," 

 (meaning also probably formaldehyde) , then in Miiller's iluid 

 for a week in an oven at 37° C. 



Van Gieson [Anat. Anz., x, 1895, p. 494) has used 

 " solutions of formalin of 4, 6, and 10 per cent.," followed 

 by 95 per cent, alcohol. Myelin was found to be well 

 preserved. 



Lactti (c/. Zeit. wiss. Mik., xii, 1895, p. 32) has had good 

 results with " 20 per cent, solutions of formol." 



Fish [Proc. Amer. Mic. Soc, xvii, 1895, ]>.319) recommends: 

 Water ... . 2000 c.c. 



Commercial formalin ... 50 „ 



Sodium chloride . . . .100 grms. 



Zinc chloride . . . . ' 15 „ 



Brains should be left iu this mixture for a week or ten days 

 or more, then transferred to a solution of water 2000 c.c, 

 formalin 50 c.c, in wliich they may remain indefinitely if 

 the jar be kept tightly covered. 



Pa[;ker and Floyd [Anat. Anze'hjer, Bd. ix, 1895, p. 150) 

 advise (for sheep's brains) a mixture of — 



Alcohol 95 per cent. . . . G volumes 



Formol 2 per cent. . 4 „ 



Brains may be kept for months in the mixture (iJiid., 

 1806, p. 568). 



Flatau [Anaf. Anz., xiii, 1897, p. 323) finds that brain 



