220 Modern Microscopy 



moisture than gum arable, which alternately contracts 

 and expands with changes of weather, and often fractures 

 delicate forms. Powdered gum tragacanth should be used 

 in the preparation of the mucilage. Put a small quantity 

 of the powdered gum in a bottle with sufficient spirit of 

 wine to just cover it. Add a small crystal of thymol or a 

 few drops of clove-oil, or oil of cassia, as an antiseptic, then 

 fill the bottle with distilled water and set it by for some 

 hours. The gum will form a thick mucilage, and may be 

 used of varying thicknesses according to the size of the 

 foraminifera. For most forms it should be of about the 

 consistency of cream, and it may be used liberally in 

 mounting, as it shrinks very much in drying. 



The same gum diluted to a watery consistency can be 

 used as a fixative for foraminifera mounted in balsam. 

 If the slide is thoroughly dried before the balsam is added 

 the gum becomes quite invisible. 



For very large and heavy foraminifera, seccotiae or some 

 other liquid glue may be used with advantage, gum not 

 being of sufficient strength to hold them safely. 



Many fossil foraminifera and recent forms from some 

 localities have the internal chambers filled with mineral 

 infiltrations, either glauconite or pyrites. These internal 

 casts reproduce more or less perfectly the shape of the 

 sarcode body of the animal. They may be obtained by 

 decalcifying the specimens with very dilute nitric acid, 

 just faintly acid to the taste. To obtain perfect casts the 

 process must be carried out very slowly, adding drop by 

 drop to the watch-glass containing the specimen. When 

 decalcification is complete the resulting cast should be 

 carefully removed with a pipette, and deposited in a spot 

 of gum on a slip. They will not stand transference with 

 a brush without damage. 



