INTRODUCTION. 



xlix 



Both dammar and Canada balsam render tissues much more transparent than glycerine. 



All traces of water must be removed from the sections before they can be mounted in dammar 

 or Canada balsam. This is done by immersing them for five or ten minutes in absolute 

 alcohol. 



METHOD OF MOUNTING IN DAMMAR. 



When a section is to be mounted in dammar all water must be got rid of. Place the 

 section in absolute alcohol for five or ten minutes, until all the water is removed. Transfer it 

 for the same period to oil of cloves or turpentine, preferably the former, which expels the 

 alcohol, and renders the section quite transparent. These operations can all be accomplished on 

 a slide thus, Float out the section on to the slide in water (p. xxvi) ; remove the water with 

 blotting-paper, add absolute alcohol to remove the remainder of the water ; after a few minutes 

 soak up the alcohol with blotting-paper, and with a stiff brush insinuate a drop of oil of cloves 

 under the section. The clove oil gradually rises through the section, expels the alcohol, and 

 renders the section quite transparent. This process ought to be observed with a low power 

 under the microscope. Remove the surplus clove oil with blotting-paper, add a drop of the 

 dammar mounting fluid, apply a cover, and the preparation is finished. 



LABELLING AND PRESERVING SECTIONS. 



After mounting, each section must be properly labelled (p. xxvi), and laid flat in a tray, 

 and preserved from dust. 



METHODS OF SEALING UP THE PREPARATIONS FOR 



PRESERVATION. 



Each preparation has still to be sealed. This is done by placing some kind of cement over 

 and round the margin of the cover-glass. After several days the specimens mounted in dammar 

 and Farrant's solution will be ready for sealing up. This is best done by means of a turntable, 

 which consists of a brass disc, at least three inches in diameter, and rotating on a pivot. 

 The upper surface of the disc has on it a series of concentric rings, corresponding to the different 

 sizes of cover-glasses used. The disc is rotated by means of the forefinger of the left hand 

 acting on a small milled head placed underneath. The slide is placed on the disc, accurately 

 centred and fixed in position by two clips, which ought to be made of bent steel spring 

 in preference to brass. A camel-hair or 

 goat-hair brush is dipped in the cement, 

 and whilst the disc is rotated a ring of the 

 cement is run round and over the margin 

 of the cover. This ought to be done 

 twice or thrice, until a sufficiently strong 

 ring is formed. In selecting a turntable, 

 see that the disc is heavy and wide enough 

 to admit the largest slide under the clips. 

 The disc must be heavy, and should rotate 



Fig. 22. MODIFIED TURNTABLE. 



steadily and easily ; and this is best secured by having the pin or pivot on which it rotates made 



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