508 HISTOLOGY 



Colorless pieces of damar are dissolved in xylol and filtered. If 

 the solution is too thin, evaporate to the proper consistence; if too thick, 

 add more xylol. The proper consistence is that of a thin syrup. 



A solution in chloroform should be prepared in similar manner for 

 use with osmium preparations. 



After paraffin sections have been cleared (3 to 5 minutes), the excess 

 of clearing agent is drained away and the surface of the slide outside the 

 sections is wiped off. The section must not be allowed to become dry. 

 A drop of damar solution is placed at once upon the section and a cover 

 glass is carefully lowered over it. With all preparations, whatever the 

 mounting medium may be, the cover glass should be lowered in the 

 following manner. It is held over the specimen and its left edge is first 

 brought into contact with the slide; a needle held in the left hand holds 

 this edge in position. Another needle held in the right hand with its 

 point beneath the right edge of the cover enables one to have perfect 

 control of the cover glass while it is being lowered. The contact between 

 the cover glass and the mounting medium spreads gradually from left 

 to right as the cover is lowered, expelling the air as it advances. If air 

 bubbles are caught in the medium, the cover may be alternately raised 

 and lowered a little until they escape, but once the cover is flat upon 

 the specimen it should not be lifted. The cover glass should be some- 

 what larger than the specimen so as to extend beyond it on all sides. 



Celloidin sections which have been cleared in oil are floated over 

 the blade of a spatula placed in the oil, and are spread out flat upon it 

 with the aid of a needle. They are then transferred to a clean glass 

 slide, being pulled from the spatula with the needle. They should be 

 moved to the exact center of the slide, if the preparations are to look 

 well, and then the oil is removed by placing two thicknesses of filter 

 paper over the section and pressing upon it quite firmly; at the same 

 time the section is made smooth. A drop of damar is then placed upon 

 the section before it dries, and the cover glass is applied as described in 

 the preceding paragraph. 



Damar mounts are then labelled and may be placed in a drying 

 oven with a temperature of 35-40 C. They may be used after a few days, 

 but the damar is not thoroughly hardened for a considerable time. 



SLIDES AND COVER GLASSES. 



Slides should be of colorless glass with ground edges. For ordinary 

 use, slides measuring i X3 inches (26 X 76 mm.) are preferable. Occasion- 

 ally, as in mounting serial sections, or large sections of the central nervous 

 system, wider slides are needed. Thick slides are preferable to thin 

 ones. 



