The Microscope. 21 



tried by an arm}^ of microscopical workers, and then stick as 

 fast to it as it shall stick to the slip and the cover glass. You 

 will learn by the experience that has always been the best 

 teacher, what are the qualities of the cement, how it must be 

 treated to have it always act its best, and how it must be kept 

 so that it may be disposed to do that best. All the innumerable 

 cements in the market and in the books, demand good treatment 

 or they will do poor work or none. If left to themselves without 

 any attention for months, they will not be in a condition to re- 

 spond to your calls. They are all made with volatile ingredients 

 so that they shall dry rapidly, and they preserve this quality 

 when they are left to themselves for a long time. The volatile 

 matters will escape through the stopper, the cement in thebettle 

 will become as hard as a rock, and the microscopist that uses it 

 but seldom and neglects it in the meanwhile, will be disgusted. 

 Cements should be looked after occasionally to see that they are 

 not dr3ang away. 



There is another annoyance that the microscopist has to con- 

 tend with and one that should not be required of him. Most of 

 the cements and mounting media bought of the dealers are in 

 bottles with cork stoppers. The stoppers should be of glass. 

 When the cement gets a little hard for the want of attention, or 

 when a little has been left on the neck of the bottle, the cork 

 sticks fast with a firmness worthy of a better cause ; and to get 

 it loose it must be twisted and bored and torn, the result being 

 that the cement or the mounting medium is filled with cork cells 

 that are sure to give trouble. If the stoppers were of glass, 

 this cork cell nuisance would be obviated, and if the glass stop- 

 pers had any tendenc}^ to stick fast in the neck, as they probably 

 would if a drop of cement were left there, this might be pre- 

 vented by slightly smearing them with a little vaseline. This 

 is a good application for corks in cement bottles. Rub a little 

 vaseline on the cork and its tendenc}' to stick and so to destroy 

 the microscopist's disposition, will be reduced, and the volatile 

 matters in the cement will evaporate no faster than with ordi- 

 nary stopers. 



It is generally best to fasten down the cover glass with the 

 cement used to make the cell. There are some rare exceptions 

 to this rule, the most common being in the use of some ornamental 

 colored material as a finishing touch to the mount. And it not 



