REAGENTS. 105 



alcohol into balsam. Balsam hardens gradually and hence the 

 slide is finished when the cover glass is placed on. 



DAMMAR. This is a resin from which solutions are made 

 similar to those of Canada balsam, the same kind of solvents 

 being used. 



GLYCERIN-GELATIN. This is a very convenient medium and is 

 often used for mounting vegetable sections. Preparation: 42 

 cc. water, 38 cc. glycerin, 7 grams gelatin, 1 gram carbolic acid. 

 Soften the gelatin (best French or German) in the water two 

 hours, add the glycerin and warm ; add the acid, warm and stir 

 one-quarter hour. Filter hot through glass wool and let cool. 

 It is solid when cold, but melts at 35 to 40 C., and will keep 

 for y^ars. Before mounting in this medium, tender objects 

 must be gradually brought from weaker to strong glycerin. 

 The gelatin is then melted, a drop placed on a warm slide, the 

 section, freed from most of the adhering glycerin, placed in it 

 and covered with a warm cover glass. When cold the gelatin 

 solidifies. The slide should then be "ringed" with a circle of 

 cement at the edge of the cover glass. This is done by means of 

 a centering turn-table, a camel's hair brush dipped in the cement 

 being held at the edge of the cover glass while the slide rotates 

 with the turn-table. 



Carmine-stained sections cannot be mounted in gelatin as the 

 carmine is soluble in it. 



FARRANT'S MEDIUM. Equal parts by weight of gum acacia, 

 saturated solution of arsenous acid and glycerin. Soak acacia 

 in solution of arsenous acid for several days, then add the 

 glycerin. Avoid shaking, which causes air-bubbles. The same 

 method of mounting is employed in this as in the case of gly- 

 cerin-gelatin. Slides should be finished with a ring of cement. 



GLYCERIN. This is used sometimes as a mounting medium, 

 but is troublesome on account of the difficulty of enclosing it 

 with cement. 



FLUIDS FOR TEMPORARY MOUNTING OF OBJECTS. 



Water is oftenest used. Glycerin, either concentrated or 

 diluted to various degrees, is an excellent medium and very 

 often used. A good fluid is a mixture of equal parts by volume 

 of glycerin, alcohol and water. 



OTHER MICRO-REAGENTS. 



SULPHURIC ACID. Strong acid diluted with one-fourth its 

 bulk of water. 



PHENOL (CARBOLIC ACID). Used as a clearing agent, also for 

 dehydrating specimens when it is not desired to use alcohol. 



