Foraminifera 



DRY WHOLEMOUNTS 



19 



cumulated decantations are allowed to 

 settle for about 20 miinitos after the last 

 batcli has been added and the suj)ernatant 

 water poured off. Add carefully about 

 twice as much nitric acid as there is sludge 

 and boil for 20 minutes. Again wash with 

 water, allow to settle antl decant. Now 

 carefully add twice as much 10% potas- 

 sium hydroxide as there is sludge, boil for 

 20 miiuites and again wash by decanta- 

 tion. The material is now nearly clean — if 

 it is not, repeat the nitric acid-potassium 

 hydroxide cycle. 



Concentrate the nearly clean skeletons 

 and then cover them with their own vol- 

 ume of ammonium hydroxide. Stir at 

 intervals for about 10 minutes, then 

 slowlj^ add an equal volume of nitric acid. 

 Wash thoroughly by decantation and ex- 

 amine the skeletons; if they are not now 

 clean, repeat the ammonium hj-droxide- 

 nitric acid cycle. Concentrate the sludge 

 as much as possible, wash it thoroughly 

 with 95% alcohol, and then either allow 

 to dry for strewn slides or store in alcohol 

 and make balsam mounts in the manner 

 described in Chapter 6. 



After the foraminiferan tests or radio- 

 larian skeletons are accumulated in a small 

 watch glass, they should be dry and quite 

 free from any of the reagents used to clean 

 them. It is also necessary to have ready 

 on the bench a binocular dissecting micro- 

 scope, two fine sable brushes, sHdes on 

 which cells have already been cemented, 

 and a container of mucilage of gum 

 tragacanth. 



The author prefers to make all forami- 

 niferal mounts in cells prepared from 

 rings of vulcanite with bottoms of black 

 paper. These should have been prepared 

 the day before in the following manner. 

 First take the required number of slides 

 and clean them thoroughly. It is not nec- 

 essary for the slides to be chemically clean 

 — it is necessary only that the slide should 

 be grease-free. A simple method of de- 

 greasing slides is to take a commercial 

 scouring powder, of the type used for 

 household purposes, and make it into a 

 paste with water. This paste is smeared 

 Hberally on all surfaces of the required 

 number of slides which are then dried. 

 When the shde is dry, the scouring powder 

 is removed by vigorous rubbing with a 



soft cloth. While the slides are drying, the 

 retpiired number of vulcanite cells are laid 

 out and a piece of fine sandpaper secured. 

 Each cell is held on the sandpaper with 

 the ball of the first finger and rubbed, 

 with a circular motion, until all the lower 

 surface has been abraded. The cell is then 

 turned over and the process repeated. One 

 side of the cell is then given a thin coat of 

 gold size and placed with firm pressure on 

 the center of a glass shde, which should 

 then be left for three or four days. Any 

 gold size which has been pressed out of the 

 inner surface should be removed with the 

 edge of a sharp pointed scalpel. A number 

 of disks of black paper of the required size 

 are then taken, coated on one side with 

 any satisfactory adhesive, and pressed 

 onto the bottom of the cell. It must be 

 remembered that the cell should be of 

 such a size that the coverslip, when laid on 

 top, does not reach to the outer edge of the 

 cell but only halfway across it. This may 

 conveniently be done by using a %-inch 

 cell with an 18-milhmeter covershp. 

 The thickness of the cell selected is not of 

 major importance but the writer usuall}^ 

 prefers about }i2 of an inch when mount- 

 ing Foraminifera. 



Let us suppose first that it is desired to 

 prepare, from the materials at hand, an 

 ordinary strewn shde hke those sold by 

 biological supply houses. It is only neces- 

 sary to moisten slightly the paper at the 

 bottom of one of the prepared cells and to 

 smear mucilage of tragacanth liberally 

 over the surface. Plenty of tests are 

 thrown onto the mucilage and the shde is 

 placed on one side for about 10 minutes to 

 dry. As soon as the mucilage is dry, the 

 slide is inverted over the watch glass con- 

 taining the tests and tapped sharply with 

 the forefinger. This will cause all those 

 tests which have not become attached to 

 the mucilage to fall back into the stock, 

 and will usually leave a continuous coat of 

 foraminiferal tests over the black paper. 



It is generally, however, more satis- 

 factory to mount selected tests in the re- 

 quired position. In this case, the black 

 paper on one of the prepared slides is 

 thoroughly moistened and a fine sable 

 brush is used to place small portions of 

 mucilage of tragacanth in the positions 

 which the selected tests are to occupy. 



