CLEARING AGENTS MOUNTING MEDIA 35 



half grams of carmine are rubbed up with a little water, and strong 

 ammonia added, a drop at a time, till the carmine is dissolved. 

 Then filter. Five grams of gelatin having previously been dis- 

 solved in water, add the carmine solution. Now neutralize the 

 carmine -gelatin exactly with acetic acid. As the neutral point is 

 approached, the acid must be diluted and added cautiously; 

 filter. 



CLEARING AGENTS 



The commonest method of preparing sections is to mount them 

 finally in Canada balsam. Staining is usually performed in watery 

 solutions. Water does not mix with balsam. After staining, 

 therefore, the water is to be removed with alcohol, which has an 

 affinity for water. The alcohol must in turn be removed with some 

 substance which will mix with balsam. The various fluids used 

 for clearing have this property, and also make the tissue trans- 

 parent. ANILINE OIL is a clearing agent which will itself remove 

 water from the tissues without the use of alcohol. It does not dis- 

 solve celloidin. It extracts the aniline colors, however. XYLOL can 

 only be used when dehydration is perfect. It does not dissolve 

 celloidin, nor extract the aniline dyes. It is often used mixed with 

 one -third of its volume of carbolic acid CARBOL-XYLOL. When an 

 agent that will not dissolve celloidin is desired, a cheap and excel- 

 lent substitute for the last is the CARBOL- TURPENTINE of Gage: 



Carbolic acid crystals (melted) 40 c.c. 



Oil of turpentine CO c.c. 



The essential oils and CREOSOTE are used frequently for clear- 

 ing, for example, the OILS of ORIGANUM, of BERGAMOT, and of 

 THYME. OIL OP CLOVES is used very extensively, but it has the 

 property of removing the aniline dyes quite rapidly, and it dissolves 

 celloidin. It may be used to clear celloidin sections, except the 

 most delicate, if care be used. Delicate sections should be cleared 

 on the slide. Other sections may be placed in a small dish of the 

 clearing fluid. 



MOUNTING MEDIA 



CANADA BALSAM is the medium most used for the permanent 

 preservation of microscopical preparations. It should be dissolved 

 in xylol, which does not affect the aniline stains. 



