112 Journal of Comparative Neurology. 



overcome some difficulties in the way of securing stable 

 preparations. 



"The sections, before they are permanently brought into 

 gum damar or Canada balsam, must first be treated successively, 

 according to the classical method, with absolute alcohol and 

 some clearing fluid. Each of these steps requires an especial 

 care not necessary with ordinary preparations. 



" (a) Treatment ivith absolute alcohol. The only rule to be 

 especially noticed here is that the sections must be very care- 

 fully dehydrated by bringing them into three or four changes 

 of pure absolute alcohol. This is the only principal rule in or- 

 der to obtain a long preservation, for the more accurately and 

 carefully the dehydration is carried out, thereby freeing the 

 tissue from the last trace of silver nitrate, the more one can rely 

 upon the preparations remaining clear a long time. 



'• {b) Clearing. The sections to be mounted must first be 

 brought, for clearing, from absolute alcohol into creosote, 

 where they remain some minutes, and then into turpen- 

 tine. In the latter they can remain a long while. The selec- 

 tion of these two substances and their consecutive use is another 

 aid to securing a long preservation. Among many other sub- 

 stances tried for clearing I have also found oleum origani ^ for 

 my method very useful, but I have found no sufficient ground 

 for abandoning the first mentioned fluids. The sections usually 

 remain in turpentine only lo to 15 minutes but may remain 

 there longer. 



" {c) Ccfinpletion of the microscopical preparations. For per- 

 manent preservation the sections are brought from turpentine 

 into damar which, after many comparative tests, I have found 

 better adapted for this purpose than Canada balsam. I must 

 here call attention especially to a peculiar treatment of the sec- 

 tions ; contrary to the usual custom, I do not cover the prepar- 

 ations with a cover glass. When the sections are covered in 

 the usual way with a cover glass, they begin after a time to turn 



' This oil, followed by washing in xylol instead of turpentine, is pre- 

 ferred by the writer. 



