MOUNTING- 479 



of liquid still surrounding the object is to be carefully drawn oft' by 

 blotting-paper, care being taken not to touch the object with it (as 

 its fibres are apt to adhere) or to leave any loose fibres on the slide. 

 Before the object is covered, it should be looked at under a 

 dissecting or mounting microscope, for the purpose of improving (if 

 desirable) its disposition on the slide, and of removing any foreign 

 particles 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 011 the slip or cover and allowed to spread 

 out. The cover being then taken up with a pair of forceps must be 

 inverted over the slide, and brought to touch it at one part of its 

 margin, the slide being itself inclined in the direction of the place 

 of contact, so that the medium dc.Qumulates 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 com- 

 pletely saturated. If air-bubbles should unfortunately show them- 

 selves, the cover must be raised at one margin, and a further quantity 

 of the medium deposited. 



If, again, there are no air-bubbles, bu^ 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 mount- 

 ing may be completed. Any excess of the medium must first 

 be removed. If glycerin 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's-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 glycerin 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, and the preparation ' sealed ' by a ring either of gold-size 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 glycerin jelly. This 

 ' ringing ' should be repeated two or three times ; and if the pre- 

 paration is to be viewed with ' oil-immersion ' lenses, it should be 

 finished off with a coat of HolhVs glue or Bell's cement,, which are 

 not attacked by cedar oil. Until the cover has been perfectly secured, 

 a slide carrying a glycerin preparation should never be placed in an 

 inclined position, as its cover will be almost sure to slide by its own 

 weight. If glycerin jelly or Fan-ants' medium has been employed, 



