302 



PRACTICAL MICROSCOPY. 



placed above each other without coming in contact with 

 the springs. 



This board may be found of much use, but it is certainly 

 better in many instances to have small independent clips 

 capable of being placed in the hot chamber, air-pump, and 

 similar situations with the slide itself. Many objects may 

 be mounted in gum resins, and the dammar and benzol will 

 perhaps be the best substance generally for objects requiring 

 to be shown with the aid of the polariscope. 



Sometimes with gum resins a source of annoyance is the 

 appearance after a time of a white cloudiness, completely 

 ruining many otherwise carefully mounted specimens. 

 This is caused by dampness, or the presence of fatty 

 matters not carefully removed before applying the balsam. 

 If the foregoing instructions be carefully followed this 

 mishap can scarcely happen. 



FIG. 247. 



Cotton fibres and sections of the same, shown in Figs. 247 

 and 248, make good polariscope objects when mounted in 



FIG. 248. 



dammar and benzol ; they should be soaked in spirit to 

 remove water, transferred to benzol and mounted direct 

 from that fluid. 



Dust and dirt are the greatest enemies of the micro- 

 scopist, and every operation which can be done under cover 



