178 THE USE OF THE MICROSCOPE 



be much used, the dammar or paraffin at the edges may 

 be covered with shellac or with clear cellulose lacquer. 

 Temporary preparations, instead of being in liquid, can 

 sometimes be mounted in agar jelly with an antiseptic. 

 This is easier to seal than a liquid. Mounts in immersion 

 oil, after hardening at the edges, can be sealed with cellulose 

 lacquer. 



Care of the Preparations. — Iron-acetocarmine prepara- 

 tions seem to spoil soon in direct sunshine, and apparently 

 even diffused light is prejudicial. They are said to keep 

 well over ice. At any rate, all stained preparations should 

 be kept in the dark when not being examined, unless 

 purposely exposed for partial fading. The trays with 

 the slides flat are superior to racks ; because the slides can be 

 looked over, and there is no sinking of loose objects to one 

 side. Covers often require to be cleaned and polished before 

 the specimen is looked at, and this matter should be attended 

 to each time. The upper surface of the cover-glass is part 

 of the optical system of the microscope. The writer finds 

 it best to clean off immersion oil while the slide is on the 

 stage, immediately after removing the oil-immersion 

 objective. Then either a dry or a water-immersion objec- 

 tive can be used forthwith, if needed. 



It should not be forgotten that the object of microscopical 

 work is to accumulate knowledge, and not, primarily, a 

 collection of well-stained preparations. So, temporary 

 preparations should be used as freely as possible, and even 

 well-stained sections need only be preserved, after they have 

 been studied, when they are wanted for future reference or 

 to show others. 



Care of the Covers. — The famihar covers, long made 

 by Chance Brothers, of hard slightly greenish crown 

 glass, are sometimes covered with a crystalline film. This 

 can be cleared off immediately by applying a drop of 

 60 per cent acetic acid to each side of the cover. After 

 wiping, they are usable forthwith for ordinary work. 

 Nitric or chromic acid is used to dissolve organic matter 

 from cover-glasses. After practice, cover-glasses can be 



