PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS. 213 



that may be accidentally present. A drop of the medium (liquefied, if 

 necessary by a gentle warmth) is then to be placed upon it, and another 

 drop placed on the cover and allowed to spread out. The cover being 

 then taken up with a pair of forceps, must be inverted over the object, 

 and brought to touch the slide at one part of its margin; the slide being 

 itself inclined in the direction of the place of contact, so that the medium 

 accumulates there in a little pool. By gently letting down the cover, a 

 little wave of the medium is pressed before it; and, if enough of the 

 medium has been deposited, the whole space beneath the cover will be 

 filled, and the object completely saturated. If air-bubbles should unfor- 

 tunately show themselves, the cover must be raised at one margin, and a 

 further quantity of the medium deposited. If, again, there are no air- 

 bubbles, but the medium does not extend itself to the edge of the cover, 

 the cover need not be raised, but a little may be deposited at its edge, 

 whence it will soon be drawn in by capillary attraction, especially if a 

 gentle warmth be applied to the slide. It will then be advantageous 

 again to examine the preparation under the Dissecting Microscope, for it 

 will often happen that an opportunity may thus be found of spreading it 

 better, by the application of gentle pressure to one part or another of the 

 covering-glass, which may be done without injurious effect either with a 

 stiff needle or by a pointed stick, a method whose peculiar value, when 

 viscid media are employed, was first pointed out by Dr. Beale. The slide 

 should then be set aside for a few days, after which its mounting may be 

 completed. Any excess of the medium must first be removed. If Gly- 

 cerine has been employed, much of it may be drawn off by blotting-paper 

 (taking care not to touch the edge of the cover, as it will be very easily 

 displaced); and the remainder may be washed away with a camel-hair 

 brush dipped in water, which may be thus carried to the edge of the cover. 

 The water having been drawn off, a narrow ring of liquefied glycerine- 

 jelly may be made around not on the margin of the cover (according 

 to the suggestion of Dr. S. Marsh) for the purpose of fixing it before the 

 cement is applied; and when this has set, the slide may be placed on the 

 Turn-table ( 176), and the preparation ' sealed ' by a ring either of Dam- 

 mar or of Bell's cement, which should be carried a little over the edge of 

 the cover, and outside the margin of the ring of glycerine- jelly. This 

 'ringing' snould be repeated two or three times; and if the preparation 

 is to be viewed with 'oil-immerson' lenses, it should be finished off with 

 a coat of Hollis's glue, which is not attacked by cedar-oil. Until the 

 cover has been perfectly secured, a slide carrying a glycerine preparation 

 should never be placed in an inclined position, as its cover will be almost 

 sure to slide by its own weight. If Glycerine-jelly or Farrants's medium 

 have been employed, less caution need be used, as the cover-glass, after a 

 few days' setting, will adhere with sufficient firmness to resist displace- 

 ment. The superfluous medium having been removed by the cautious 

 use of a knife, the slide and the margin of the cover may be completely 

 cleansed by a camel-hair brush dipped in warm water; and when quite 

 dried, the slide, placed on the Turn-table, may be sealed with Gold-size, 

 any other Cement being afterwards added either for additional security 

 or for 'appearance.' 



209. When, on the other hand, the Section or other preparation is to 

 be mounted in a Resinous medium, it must have been previously prepared 

 for this in the modes already % described ( 190, 191), which will present 

 it to the mounter either in Turpentine or some other essential oil, or in 

 Alcohol. From either of tliejo it may bo transferred to the slide by the 



