MOUNTING IN BALSAM AND GLYCERIN 201 



and xylol : (1) one fourth xylol and three fourths absolute alcohol ; (2) half 

 and half xylol and absolute alcohol ; (3) three fourths xylol and one fourth 

 absolute alcohol. Even the most delicate material of algse and fungi can 

 generally be carried without shrinkage into pure xylol if passed through 

 these grades, being left an hour or more in each. Once in xylol, material is 

 safe from shrinkage, and it may be left in this reagent indefinitely. It is 

 absolutely essential for good results that the dehydration be perfect. Small 

 objects should be examined throughout the process to determine the exact 

 time of any cell shrinkage, which may be corrected with greater care. 



After being in clove oil a short time (from five to fifteen minutes), or 

 in xylol a much longer time (several hours), the material is transferred to 

 Canada balsam on the slide. The balsam should be so diluted with xylol 

 that it drops readily from a glass rod. A cover glass is then gently lowered 

 over the object with the point of a needle. The balsam will gradually harden 

 as the xylol dries out. Air bubbles need give no concern ; they will work 

 out to the edge of the cover glass as the balsam hardens. When balsam 

 thickens in its bottle xylol should be added ; the cloudiness which may 

 develop will soon pass away. 



188. Mounting in glycerin. Material is transferred from water to a con- 

 siderable quantity of a 10% aqueous solution of glycerin in a watch glass. 

 This should not cause shrinkage. The watch glass is then protected from 

 dust and the water allowed to evaporate until the solution is about as thick 

 as pure glycerin. The material is now ready to be mounted and will be so 

 soft that it can be easily teased apart. A small drop of the solution is placed 

 on the slide, the material arranged in it, and a clean cover glass with one 

 edge resting on the slide is carefully lowered with a needle until the glycerin 

 runs out to the edge on all sides. This must be done so carefully that no 

 bubbles of air are inclosed. 



Practice will determine the amount of glycerin necessary to fill the space 

 under the cover glass, which should not be more than five eighths the width 

 of the slide. The less glycerin the better. The glycerin should not run 

 out beyond the edge of the cover glass, although a small amount may be 

 wiped away with a cloth moistened in alcohol. On no account must the 

 glycerin be allowed to run over the edge of the cover glass ; such a prepara- 

 tion is worthless." The slide is now ready to be sealed, or it may be laid away 

 to allow the glycerin to become somewhat more dense. 



The best cement is gold size. This should not be so thick that it cannot 

 be easily spread with a brush. If too thick, thin with oil of turpentine. The 

 gold size is generally applied at the edge of the cover glass while the slide is 

 whirling on a turntable. A thin ring should be laid three eighths of an inch 

 wide, half on the slide and half over the edge of the cover glass, thus seal- 

 ing the glycerin within a chamber. The sealing will not be perfect unless 



