CHAPTER VI. 



DE-ALCOHOLISATiON AND CLEARING AGENTS. 



105. Introductory Remarks. De-alcoholisation agents* are 

 liquids employed for the purpose of getting rid of the alcohol 

 in which preparations are generally preserved, and facili- 

 tating the penetration of the paraffin used for imbedding, or 

 the balsam or other resinous medium in which preparations 

 are, in most cases, finally mounted. Hence all of them 

 must be capable of expelling alcohol from tissues, and must 

 be at the same time solvents of Canada balsam and the other 

 resinous mounting media. The majority of them are essen- 

 tial oils. 



Clearing agents are liquids whose function it is to make 

 microscopic preparations ^transparent by penetrating amongst 

 the highly refracting elements of which the tissues are com- 

 posed, the clearing liquids themselves having an index of 

 refraction superior, or equal, or, at all events, not greatly 

 inferior to that of the tissues to be cleared. Hence all 

 clearing agents are liquids of high index of refraction. 



The majority of de-alcoholisation agents being also liquids 

 of high refraction, it follows that they serve at the same time 

 for de-alcoholisation and for clearing ; and in consequence 

 it has come about that de-alcoholisation agents are generally 

 spoken of as clearing agents. (The expression " de-alcoholi- 

 sation agents " is here used for the first time as a correlative 

 of the "Vormedien" of APATHY (Mikrotechnic) , and the 

 " Vorharze " of the Grundzuge, due to MAYER ; in previous 

 editions clearing agents and de-alcoholisation agents were 

 indiscriminately spoken of as clearing agents.) But that 

 practice is not strictly correct, for not all clearing agents are 

 solvents of tlie resins, and not all de-alcoholisation agents 

 can serve as clearers. For instance, glycerine is a clearing 

 agent, but cannot be used to prepare objects for paraffin or 



