DE-ALCOHOLISATION AND CLEARING 71 



alcohol of 90 per cent., or even 80 per cent. One part xylol and 

 4 terpineol has been much used lately. 



148. Carbolic Acid. Best used in concentrated solution in 

 alcohol. Clears instantaneously, even very watery preparations. 

 This is a very good medium, but it is better avoided for prepara- 

 tions of soft parts which it is intended to mount in balsam, as they 

 generally shrink by exosmosis when placed in the latter medium. 

 It is, however, a good medium for celloidin sections. 



Gage's Mixture {Proc. Amer. Soc. Micr., 1890, p. 120). Carbolic 

 acid crystals melted, 40 c.c. ; oil of turpentine, 60 c.c. 



149. Creosote. Much the same properties as carbolic acid. 

 Beech-zvood creosote is the sort that should be preferred for many 

 purposes — amongst others, for clearing celloidin sections, for 

 which it is a very good medium. Note Gray's remarks (§ 136). 



150. Anilin Oil. Common anilin oil will readily clear sections 

 from 70 per cent, alcohol, and with certain precautions (see the 

 paper by Suchannek, Zeit. wiss. Mikr., vii, 1890, p. 156, or the 

 third edition of this book), objects may be cleared from watery 

 media without the intervention of alcohol at all. 



In recent years the use of anilin oil, for clearing delicate tissues, 

 e.g. mammalian testicular material (§ 629) has become widespread 

 because the higher grades of alcohol may be avoided. It is to be 

 noted, however, that it should not be used following osniic acid fixation. 

 Ordinarily, one begins with tissues in 50 or 70 per cent, alcohol and 

 gradually replaces the alcohol with anilin oil. After clearing the 

 anilin oil should be washed out of the tissue by two or three changes 

 of chloroform, or some similar reagent, because it does not mix 

 well with paraffin. 



On standing commercial anilin tends to discolour through 

 oxidation, and if exposed to air, it may absorb water. While the 

 change of colour does not spoil it for use, the lighter shades are to 

 be preferred. (Old oil should be redistilled.) 



Anilin is chiefly used for clearing celloidin sections. It ought, 

 however, to be soaked out before mounting by something else 

 (chloroform or xylol for instance for some hours), as if not removed 

 it will brown both the tissues and the mounting medium. 



151. Chloroform. For clearing tissues before imbedding chloro- 

 form has long been a favourite reagent in many laboratories. 

 It is an excellent de-alcoholisation agent, as it will take up a good 

 deal of water, if any be left in the tissue and it seems to render 

 many tissues less brittle than xylol. The one drawback of chloro- 

 form is that it does not penetrate well, and its use should therefore 

 be restricted to small objects which are easily penetrable. 



152. Xylol, Benzol, Toluol. Too volatile to be recommendable 

 as clearing agents in which it is desired to examine specimens, 

 but very useful for clearing small objects. 



