482 PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS 



continue when it may have once commenced. "\Vheii cement-cells, 

 are employed for this purpose, care must be taken that the surface 

 of the riii"- is perfectly flat; so that when the cover-glass is laid on 

 110 tilting is produced by pressure on any part of its margin. As a 

 general rule, it is desirable that the object to be mounted should be 

 steeped for a little time previously in the preservative fluid employed. 

 A sufficient quantity of this fluid being deposited to overfill the 

 cell, the object is to be introduced into it either with the forceps or 

 the dipping tube; and the slide should then lie examined on the 

 dissecting microscope that its entire freedom from foreign particles 

 and from air-bubbles may lie assured, and that its disposition may 

 be corrected if necessary. The cover should then be laid on very 

 cautiously, so as not to displace the object; which in this case is 

 best done by keeping the drop highest in the centre, and keeping 

 1 IK- cover parallel to the slide whilst it is being lowered, so as to 

 expel the superfluous fluid all round. This being taken up by the 

 syringe, the cement ring and the margin of the cover are to be 

 dried with blotting-paper, especial care being taken to avoid drawing 

 oft' too much liquid, which will cause the gold-size to run in. It i* 

 generally best to apply the first coat of gold-size thin, with a very 

 small and flexible brush worked with the hand ; this will dry suffi- 

 ciently in an hour or two to hold the cover whilst being ' ringed ' 

 on the turn-table. And it is safer to apply a third coat a day or 

 two afterwards; old gold-size, which lies thicklv. being then applied 

 so as to raise the ring to the level of the surface of the cover. As 

 experience shows that preparations thus mounted, which have 

 remained in perfectly good order for several years, may be afterward* 

 spoiled by leakage, the Author strongly recommends that to prevent 

 the loss of valuable specimens an additional coating of gold-size be 

 laid on from time to time. But a device of much greater value in 

 all fluid mounting is that adopted by Mr. Enock, 1 who put* a 

 metallic ring of angular section round the outside of the cell, 

 slightly overlapping the cover-glass and enclosing the rim made 

 good with cement ; this proves perfect. 



Mounting of Objects in Deep Cells. The objects which require- 

 deep cells are, as a rule, such as are to be viewed by reflected light, 

 .-mil are usually of sufficient size and substance to allow of air being 

 entangled in their tissues. This is especially liable to occur where 

 they have undergone the process of decalcification. which will very 

 probably leave behind it bubbles of carbonic acid. For the extrac- 

 tion of such bubbles the use of an air-pui up is commonly recommended ,- 

 butthe Editor lias seldom found this answer the purpose satisfactorily, 

 and is much disposed to place confidence in a method lately recom- 

 mended steeping the specimen in a stoppered jar filled with freshly 

 boiled H-iilt-r. uhich has great power of drawing into itself either air 

 Or carbonic acid. Where the structure is one which is not injured 

 by alcohol, prolonged steeping in this will often have the same effect. 

 The next point of importance is to select a cover of a si/.e exactly 

 suitable to that of the ring, of whose breadth it should cover about 



O 



wo-thirds, leaving an adequate margin uncovered for the attachment 



1 Quekett -limni. second series, vol. i. p. 4(1. 



