296 



SCIEXCE- G OSSIP. 



EXPERIENCES IN FLOATING FORAMINIFERA. 

 By Dr. G. H. Bryan. F.R.S. 



n^HE failure of my attempt* to obtain satis- 

 -■- factory results in cleaning foraminifera by 

 the method of surface flotation, elicited about two 

 years ago a series of interesting articles in Scebncb- 

 Gossep from the pen of Mr. Earland. With the 

 information obtained from these, and the experience 

 derived from the somewhat similar operation of 

 cleaning desmids. I have succeeded in securing 

 several really excellent " cleanings " of foraminifera. 

 It has seemed to me that an account of the results 

 may be of interest to your readers in explaining 

 the failures of the " flotation " method in dealing 

 with certain gatherings. I propose to consider 

 separately the several classes of material used in 

 my experiments. 



1. Fete Sponge Sand. 



The greater portion of sponge sand passes through 

 the finest gauze sieves that I possess. On intro- 

 ducing some of these fine powders into water, it was 

 impossible to prevent a thick film of the grains from 

 floating on the surface in consequence of capillarity, 

 and even when a paper funnel was used, bubbles 

 would be carried down and rise to the top with 

 some of the fine sand adhering to them. The cause 

 of failure of the flotation method was evident on 

 examining the sediment, for it contained practically 

 all the f oraminif era. which had sunk to the bottom, 

 their chambers still being filled with air. Even the 

 substitution of salt-water for fresh-water did not 

 give the foraminifera sufficient buoyancy to rise to 

 the surface. By placing the sediment in water at 

 one side of a saucer or soup plate, and shaking it. 

 the foraminifera rose to the surface of the sand ; 

 and by carefully rocking the plate they could be 

 drawn round to the other side, leaving the sand 

 high and dry behind. The foraminifera were 

 transferred to another plate, and any shells which 

 got stranded were removed by a second washing ; 

 the rejected material then consisted practically of 

 pure sand with only a very occasional f oraminif er 

 still left. The number lost in this way mnst have 

 been insignificant. 



After thns dealing with small batches of material 

 and getting rid of the bulk of the sand, the cleaned 

 material, now reduced to a very small quantity, 

 was once more washed in the same way and the 

 residual sand removed. A teaspoonful of the 

 sponge sand yielded a small pinch of cleaned 

 material, barely sufficient for mounting three very 

 pretty slides, thickly spread over f-inch covers. 

 In some cases over 50 per cent, of the total num- 

 ber of particles were foraminifera. This method 

 of washing, as applied to sponge sand eliminated 



the whole of the fine sand grains constituting the 

 great bulk of the material. It gives washings 

 rich in foraminifera, but these were mixed with 

 debris, such as broken shells, fragments of coral, 

 sponge fibre, etc. I have tried to separate these 

 by repeating the washings, but after a certain 

 stage both the foraminifera and the associated 

 particles began to separate into different sizes 

 without further selection from each other. I then 

 tried placing the washings on an inclined plane of 

 paper, but found that, so far from the foraminifera 

 separating from the debris, the larger and more 

 unsightly particles of the latter were the first to 

 skip off the paper. So I tried tapping the paper 

 from below several times, and it soon appeared 

 that the foreign bodies with comparatively few 

 of the larger foraminifera jumped the greatest 

 distance down the plane, and the material which 

 remained furthest behind, on being spread, yielded 

 slides of far greater purity than could be obtained 

 by spreading the washings in bulk. This action 

 of the inclined plane was in some respects the 

 reverse of what I had previously experienced with 

 sand from Colwyn Bay. 



2. Coarser Sponge Sittings. 



On sifting a quarter of a pound of sponge sand 

 through the same fine sieve, about a teaspoonful of 

 white grains remained, and a coarser sieve removed 

 the large fragments of shell, seaweed, and other 

 large foreign bodies mixed with the sittings. Prac- 

 tically none of the foraminifera floated in water ; 

 but by rocking in a soup-plate, as before, sufficient 

 foiaminif era for about seven or eight closely spread 

 slides were separated from the rest of the mass. 

 mixed, however, with an equal bulk of vegetable 

 debris. To separate the latter I waited till the 

 chambers of the foraminifera had filled with air. 

 and then rocked them in a soup-plate, this time 

 much more gently : and it was thus easy to draw 

 the vegetable matter away, leaving the shells be- 

 hind. The rocking process rendered it possible. 

 first, to draw the foraminifera from the sand, and 

 then the vegetable matter away from the forami- 

 nifera, the material being separated into three 

 different portions, the foraminifera constituting 

 that of intermediate density. The spread "slides of 

 these foraminifera contain hardly any foreign 

 particles, though many of the shells themselves are 

 somewhat broken 



3. Coarse Shore-sand. 



A heap of shore-sand used for building purposes 

 in this neighbourhood had been left for some week* 



