Fluid Wholemounts — Aqueous Type 



General Principles 



A fluid wholemount in an aqueous me- 

 dium is essentially a miniature museum 

 mount in which the glass jar has been re- 

 placed by a cell mounted on a microscope 

 slide. With the exception of the selection 

 of a slide — for none other than glass is 

 suitable — the choices confronting the 

 technician are very much those discussed 

 in the preparation of dry wholemounts in 

 the last chapter, though the selection is in 

 each instance different. It is necessary to 

 select successively a type of cell, a cement 

 for attaching the cell to the sUde, a cement 

 for attaching the coverslip to the cell, 

 and finally the mounting medium itself. 



Selection of a Cell 



The author prefers to use concave- 

 ground glass slides instead of cells. At 

 the present time these concave glass shdes 

 are both difficult to obtain, and unsatis- 

 factory when obtained, from American 

 sources. It is, however, possible to secure 

 in Great Britain slides into which have 

 been ground circular concavities from 9 to 

 20 milhmeters in diameter, or oval con- 

 ca\'ities in many sizes. The use of cavity 

 sUdes avoids the difficulties of attaching a 

 cell, and the slides are more waterproof 

 than any cell. It is to be hoped that Ameri- 

 can suppliers will make cavity slides avail- 

 able to technicians who wish to make 

 wholemounts in fluid media. 



If, however, cells must be used, the 

 choice is very hmited. It is a waste of time 

 to take paper and cardboard cells and to 

 endeavor, by soaking them in various 

 resins, to make them take the place of a 

 plastic or metal cell. Cells of vulcanite 

 anb tin are obtainable or may be pre- 



pared with the aid of a punch. These 

 should, before use, be flattened on both 

 sides in the manner described in the last 

 chapter. Where a very deep mount is re- 

 quired, it is better to use a glass cell which 

 can be cut from thick-walled glass tube 

 and ground flat on both faces. These cells 

 are usually only obtainable in a %-inch 

 size and care should be taken, as with 

 other cells, to make sure that the edges of 

 the coverslip selected will he on the sur- 

 face of the cell. It is difficult to seal a dry 

 wholemount, and impossible to seal an 

 aqueous wholemount, in which the edge 

 of the coverslip and the edge of the cell 

 coincide. An almost perfect relationship 

 is that of an 18-millimeter covershp to a 

 fi-ineh cell, but unfortunately both 

 18 mm. and 3-^-inch appear to be used 

 interchangeably by scientific supphers so 

 that the measurements must be checked 

 before mounting. 



When very thin objects are to be 

 mounted, a cell can be made from gold 

 size in the manner described in the last 

 chapter. 



Selection of a Cell Cement 



The selection of a cement to attach 

 the cell to the shde is of far more impor- 

 tance in aqueous fluid mounts than in dry 

 mounts. The cement must not only lje 

 capable of holding the cell firmly to the 

 glass, but must also make a waterproof 

 seal which must remain waterproof for 

 many years. In the author's experience no 

 varnish is satisfactory, and one is forced 

 to turn to the thermoplastic cements. 

 Among these marine glue (Chapter 28, 

 V 12.2 Beale 1880) or, if this is not obtain- 



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