424 CHAPTER XXXII. 



to one half its volume of absolute alcohol, and put the sections into it for 

 several minutes ; they become dark grey to black. As soon as reduction is 

 complete the sections are put for ten to fifteen minutes into 70 per cent, 

 alcohol, then brought for five minutes into solution of hyposulphite of 

 soda (about 10 parts to 50 of water), and thence into a large quantity of 

 distilled water, where they should remain for twenty -four hours or more. 

 Lastly, dehydrate in the usual way and mount under a cover. After- 

 staining with carmine, etc., may be employed. 



762. ZIMMEEMANN'S Process (Arch. mik. Anat., lii. 1898, p. 552 ; Zeit. 

 f. wiss.Mik.,xv, 1898, p. 216). Sections are brought, after silvering, from 

 alcohol into a mixture of 1 part physiological salt solution and 2 parts 

 96 per cent, alcohol. They must be kept in motion therein for ten to 

 fifteen minutes, after which they are brought into alcohol of 75 to 96 per 

 cent., in a bright light, until they have become dark. 



The Sublimate Method. 



763. GrOLGi's Bichromate and Sublimate Method (Archivio per 

 le Scienze Mediche, 1878, p. 3; Archives Italiennes de Biologie, 

 iv, 1883, p. 32 ; vii, 1886, p. 35). This method consists of two 

 processes : 1, hardening in bichromate ; 2, treatment with 

 bichloride of mercury. 



For hardening, use either a solution progressively raised 

 in concentration from 1 per cent, to 2| per cent., or Miiller's 

 solution. It is beat to take small pieces of tissue (not more 

 than 1 to 2 c.c.), large quantities of liquid, and change the 

 latter frequently, so as to have it always clear. But the re- 

 action can be obtained with much larger pieces, even entire 

 hemispheres. In this case the brain should at first be treated 

 by repeated injections of the liquid, so as to ensure as rapid 

 a permeation of the interior as possible. Fifteen to twenty 

 days' immersion will suffice, or even six to eight, but twenty 

 to thirty should be preferred, and an immersion of several 

 months is not injurious. 



The tissues when hardened are passed direct from the 

 bichromate into 0'5 per cent, solution of bichloride of mer- 

 cury. An immersion of eight to ten days therein is necessary 

 in order to obtain a complete reaction through the whole 

 thickness of the tissues (or for entire hemispheres two months 

 or more). During the bath the bichromate will diffuse out 

 from the tissues into the bichloride, which must at first be 



