PYBIDIN. 49 



87. Acetate of Lead. Both the neutral acetate (sugar of lead) and the 

 basic acetate have been used for hardening nerve tissues. ANNA KOTLA- 

 EEWSKY found that nerve-cells hardened in 10 per cent, solution of sugar of 

 lead were admirably preserved. See her " Inaug.-Diss.," in Mitth. d. naturf. 

 Ges. Bern., ]887, and Zett.f. wiss. Mik., iv, 3, 1887, p. 387. 



88. Alcohol. When used alone, alcohol is inferior as a 

 hardening agent to most of the reagents discussed above; 

 but when judiciously employed to complete the action of a 

 good fixing agent, it renders most valuable services. 90 to 

 95 per cent, is the most generally useful strength. Weaker 

 alcohol, down to 70 per cent., is often indicated. Absolute 

 alcohol is seldom advisable. You ought to begin with weak, 

 and proceed gradually to stronger, alcohol ! Large quantities 

 of alcohol should be taken. The alcohol should be frequently 

 changed, or the tissue should be suspended near the top of 

 the alcohol, in order to have the tissue constantly surrounded 

 with pure spirit (the water and colloid matters extracted from 

 the tissue falling to the bottom of the vessel). Many weeks 

 may be necessary for hardening large specimens. Small 

 pieces of permeable tissue, such as mucous membrane, may 

 be sufficiently hardened in twenty-four hours. 



89. Iodine may be used in combination with alcohol, and render service 

 through its great penetrating power. See the method of BETZ, post, Part II. 



90. Pyridin. Pyridin has been lately recommended as a hardening 

 agent (by A. DE SOUZA). It is said to harden, dehydrate, and clear tissues 

 at the same time. They may be stained after hardening by anilin dyes dis- 

 solved in the p} T ridin, or passed through water and stained by the usual pro- 

 cesses. It is said to harden quickly, and to give particularly good results 

 with brain. See Comptes Rendus liebd. de la Soc. de Biologic, 8 ser., t. iv, 

 No. 35, p. 622 ; Zeit.f. wiss. Mik., v, i, 1888, p. 65 ; Journ. Roy. Mic. Soc., 

 1888, p. 1054. 



