44 



KNOWLEDGE 



[Febbuaby, 1902. 



COLLECTING AND PREPARING FORAMINI- 

 FERA. 



By A. Eari.and. 

 (Continved from ]>■ 21.) 

 The rosiiliuini which had been set aside in a jar may now 

 be treuti'il \<y the " rockiuf; " process, for the sejtaration oC 

 the ri'iniiinlng Forainiuifera. Taking the ]i)i()to<,'ra[)hic 

 devclo|>ini,' dish, or a tin tray may be used as a substitute, 

 enous;h ot the residuum is placed in it to cover the bottom 

 to a depth of about } inch, and covered with about | inch 

 of water. If the dish is tlien rocked witli a combined up 

 and down and circuhir motion, the Foraminif(!ra will rise 

 in suspension in the water, and by a little careful manipula- 

 tion may be gathered in one corner of the dish. A sudden 

 tilt will then empty them with the water into a sieve. 

 The operation should be repeated with two or three lots 

 of water, and the material left in the dish will then be 

 found to consist almost entirely of sand. The material 

 left in this second sieve, known as " washings," is not so 

 pure as the " floatings," for it contains a large percentage 

 of broken forms and shell fragments, coal dust, and other 

 di'hris. It may be further purified, if desired, by being 

 dried and " floated " once or twice in the glass jar. 



If the floatings thus obtained contain much animal or 

 vegetable matter, as is sometimes the case, it is advisable 

 to boil them in a solution of caustic potash. This will not 

 damage the Foraminifera so long as the boiling is not 

 carried on too long, and it effectually removes the animal 

 matter, which otherwise would encourage fungoid growths. 



The processes already described are intended for recent 

 mndy gatherings. When the material is in the form of 

 dredged mud, it is first necessary to get rid of the finest 

 particles of this mud, for if the water is turbid it becomes 

 very difficult to judge the right moment for separating 

 the floating Forams. The mud should be bi-oken up into 

 small lumps, about an inch cube,and slowly but thoroughly 

 dried. It is then placed in a basin and covered with 

 water, which rapidly breaks it up into a fine mud. Such 

 specimens as may be observed floating on the surface of 

 the water may be easily removed by means of cigarette 

 papers, which ai-e placed on the surface of the water. 

 The Forams adhere to the papers, which are then carefully 

 lifted off and dried, the Forams being then brushed off 

 into a tube. Many delicate forms, which would almost 

 certainly be broken in the subsequent processes, may thus 

 be obtaine.i in a perfect state. 



The mud remaining in the basin is then washed, a 

 spoonful at a time, by placing it in a sieve of fine silk 

 gauze, through which a gentle stream of water from the 

 tap is kept running until all the fine particles have been 

 removed. The muddy water should be allowed to settle 

 in a bath, and the solid residuum then scraped out and 

 thrown away. The sandy residuum left in the sieve should 

 then be thoroughly dried, and is then ready for examina- 

 tion under the microscope, or if desired it may be further 

 purified by the floating and rocking processes already 

 described. 



Foraminifera occur in marine fossil deposits of all 

 geological ages, from the Cambriau to Post Tertiary dejiosits, 

 but they are, as a rule, of sparing occurrence until we reach 

 the Cretaceous period. The harder chalks and limestones 

 can only be studied by means of thin sections, but the 

 softer chalks, shales, and clays may be broken up by 

 drying the material in small pieces, and washing it over a 

 fine sieve in the manner just described. Floatings are 

 seldom procurable from fossil deposits owing to the weight 

 of the specimens, w-hich are generally more or less infil- 

 trated with pyrites or other mineral matter. 



Some chalks and shales which resist the disintegrating 



action of water after being dried may be broken up by the 

 action of a crystallising salt, which has been absorbed in 

 a fluid state. Acetate of soda has the most rapid action, 

 but very fair results may be obtained with common 

 washing soda. The material after being broken up into 

 small ])cllots is dropped into a boiling saturated solutifin 

 (iF the salt, and kept at this temperature for a short time to 

 allow of penetration. The salt is then allowed to cool, and 

 in cooling crystallises, the formation of the crystals 

 breaking up the outer layer of the material. On being 

 warmed the soda dissolves again in its own water of 

 crystallisation, and the crystallisation is repeated over and 

 over again until the lumps are broken up. The resulting 

 mud is then washed in the ordinary way. 



The best Foraminifera from the chalk are those obtained 

 from the interior cavities of hollow flints. They are often 

 in the most perfect state of preservation, and the chalk in 

 these cavities being of a powdery nature, they are very 

 easily cleaned. 



The cleaned material should be sifted into varying 

 degrees of fineness, and each grade kept separately in a 

 tightly corked tube, noted with locality, date, and any 

 details as to the species contained in it, which may be 

 likely to be useful for future purposes of reference. If 

 the material has been properly cleaned and dried it can 

 be kept unaltered for an indefinile period, but if jiut away 

 damp, fungoid growth will quickly set in. This can be 

 destroyed, and the material sterilisect,by aprolonged soaking 

 in spirit, the material being afterwards dried once more. 



To examine the material under the microscope a picking- 

 out tray will be necessary. This is made by covering a 

 slip of card with coarse black ribbed silk, the ribs running 

 longitudinally along the slip. A thin wooden ledge must 

 be glued round three sides of the slip to prevent the 

 Forams rolling oft' when the stage of the microscope is 

 inclined at an angle. The material is sprinkled over the 

 slip, and the ridges of silk keep the Forams from rolling 

 about. The specimens required can tben be easily selected 

 by means of a fine sable brush, moistened by drawing it 

 between the lips, and transferred to a jsrepared cell or slip. 



The best fixative for mounting Foraminifera is gum 

 tragacanth, which is almost invisible when dry, being 

 cjuite devoid of the objectionable glaze which characterises 

 gum arable. It is also much less subject to variations of 

 moisture than gum arable, which alternately contracts and 

 expands with changes of weather, and often fractures 

 delicate forms. Powdered gum tragacanth should be 

 iised in the preparation of the mucilage. Put a small 

 quantity of the powdered gum in a bottle with sufficient 

 spirits 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 mav 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 Foraminifei'a, seccotine 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 shajie of the 

 sarcode body of the animal. They may be obtained by 

 decalcifying the specimens ■with very dilute nitric acid, 



