1892.] 



THE MICROSCOPE. 



243 



the water rapidly evaporates. The slides are kept there with a 

 card-board cover over them to keep off dust, until the evaporation 

 is complete and the sections adhere to the slide. The time re- 

 quired for this varies according to the thickness of the sections ; 

 for thin sections one hour is generally sufficient for complete fixa- 

 tion, but the important point is that the paraffi7i 7nust never be 

 7nelted until the last ti'ace of water has disappeared from the 

 slide. If this premature melting happens by any accident, the sec- 

 itons are certain to peel oft'later. A few experiments enables one to 

 be sure of the point when the slides are safe. 



After complete fixation the paraffin is melted by putting the 

 slide inside the oven and then washed oft^ with turpentine or 

 xylol. 



One of the great advantages of this method is the perfect ease 

 and safety with which it allows sections on the slide to be manipu- 

 lated, so that the most various stains and reagents can be applied 

 successively to a slide, e. g.^ the complicated processes used to 

 demonstrate bacteria in the tissues can be applied, with the cer- 

 tainty, moreover, that there is nothing on the slide to be stained 

 which was not in the section. — A7nerican Naturalist^ NoveTu- 

 ber^ i8g2. 



Using Oil-Immersion Objectives. — In using these objec- 

 tives cleanliness is important. Only a small quantity of the im- 

 mersion fluid (specially prepared cedar oil) should be used, and 

 it should be wiped oft' as soon as possible when done using. 



To remove the oil, blotting-paper should be used, and then, 

 breathing on the front lens, wipe it lightly with a piece of clean, 

 soft linen. 



In order to keep the immersion fluid unchanged, it should not 

 be exposed to the air for any length of time, as exposure to the 

 air will thicken it, and so alter the refractive index. — E. Pe7inock. 



C°RRESP°nDEnCC • 



^^^ 



'mmmm^mm. 



White's Objects. — Prof. Wm. Lighton, of Omaha, Neb., 

 writes : 



•• The specimens of White's preparations you sent me are truly 

 magnificent. Nothing better can be found." 



