76 



MOUNTING AND LABELING. 



but little light is reflected from it. If it is held toward the window, 

 however, it will appear translucent. 



The third and final step is the displacement of the clearer by the 

 resinous mounting medium. 



The specimen is drained of clearer and allowed to stand for a short 

 time till there appears the first sign of dullness from evaporation of the 

 clearer from the surface. Then a drop of the resinous medium is put 

 on the object and finally a cover-glass is placed over it, or a drop of the 

 mounting medium is spread on the cover and it is then put on the 

 object.' 



It is in many ways more convenient to perform the series of displace- 

 ments on the slide. This must be done with serial sections. If the 

 preparations are not fastened to the slide, some workers perforin the 

 dehydration and clearing in separate dishes. 



§ 176. Order of Procedure in Mounting Objects in Resinous 

 Media by Desiccation. 



1. The object suitable for the purpose (fly's wing, etc.) is thoroughly 

 dried in dry air or by gentle heat. 



2. The object is arranged as desired in the center of a clean slide on 

 the centering card (PI. V., Fig. 46.) 



3. A drop of the mounting medium (§ 191) is put directly upon the 

 object or spread on a cover-glass. 



4. The cover-glass is put on the specimen with fine forceps (PI. II, 

 Fig. 14), but in no case does one breathe on the cover as when media 

 miscible water are used. 



5. The cover-glass is pressed down gently. 



6. The slide is labeled (§ 179). 



7. The preparation is cataloged and safely stored (§§ 181- 183). 



8. Although it is not absolutely necessary, it is better to seal the 

 cover with shellac after the medium has hardened round the edge of 

 the cover (§ 169 C). 



§ 177. Order of Procedure in Mounting Objects in Resinous 

 Media by successive Displacements. 



1. A suitable object is selected, for example a section of animal tis- 

 sue, and is centered on a clean slide. 



2. The slide is held in the hand and the object is dehydrated by 

 dropping upon it strong alcohol (§ 175 B). 



3. The alcohol is drained from the specimen and removed by blotting 

 paper held at the edge of the object. 



4. Two or three drops of the clearer (§ 192) are put on the object to 

 displace the alcohol (§ 175 B). 



