CLASSIFICATION OF CLEARING AGENTS. 185 



alcohol on to the clearing medium). Then put the objects into 

 the alcohol. They will sink down to the level of separation of 

 the two liquids at once ; and after some time they will be founcl 

 to have sunk to the bottom of the clearing medium. They 

 may then be removed by means of a pipette ; or the superna- 

 tant alcohol drawn off and the preparations allowed to remain 

 until wanted. 



The chief clearing agents are essential oils. A classifica- 

 tion of these is given below (No. 330, Stieda and Schieffer- 

 decker). 



The penetration of all clearing media may be hastened by 

 using them warm. Directions for clearing are given when 

 necessary under the heads of the different organs and tissues. 

 It will suffice here to advise the beginner to keep on his table 

 the following : Oil of cedar, for general use ; clove oil, for 

 making minute dissections in cases in which it is desirable to 

 take advantage of the property of that essence of forming very 

 convex drops on the slide, and of imparting a remarkable 

 brittleness to soft tissues; carbolic acid, for rapidly clearing 

 imperfectly dehydrated objects. 



330. Classification of Clearing Agents (STIEDA). Stieda's 

 experiments with essential oils led him to establish the follow- 

 ing classification : 



A. The turpentine group, capable of clearing in a short 

 time perfectly dehydrated sections, but clearing watery sections 

 only after many hours or not at all. 



Ol. Terebinthinae. 



01. Absynthii. 



01. Balsam. Copaivas. 



01. Cortic. Aurantiorum. 



01. Cubebarum. 



Ol. Fceniculi. 



01. Millefolii florum. 



Ol. Sassafras. 



Ol. Juniperi. 



01. Menthaa crispae. 



01. Origani vulgaris. 



01. Lavandulae. 



01. Cumini. 



01. Cajeputi. 



