838 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



experiment. Let us suppose that we have succeeded in bringing a 

 quantity of diatomaceous material to the state of a beautiful white 

 powder, as previously described, by the use of the bisulphate of 

 potassa, or the more easily procured substitute suggested. We then 

 proceed as follows : Procure a piece of silk about four inches square, 

 of good quality, and of very close texture ; moisten it thoroughly at 

 first, and in its depressed centre place a small portion of the fused 

 material to be cleaned ; then add to it several drops of water to bring 

 it in solution, collect the sides and corners of the silk together, twist 

 them to prevent the escape of material or fluid, compress immediately 

 above the material, and carry the pressure down gradually, without 

 however bringing the pressui-e of the fingers to the bottom part of 

 the silk ; this compression forces out the water, and with the water 

 a large percentage of the undesirable impurities contained in the 

 material, while the close texture of the silk holds back the various 

 diatoms and disks with the larger particles of sand. After the first 

 compression a few more drops of water are added, and the pressure 

 renewed as before. The silk is then turned inside out, and washed 

 by gentle shaking in a deep watch-glass to remove the diatoms, &c. 

 We now note an absence of milkiness in the product, and the cleaned 

 residue remains at the bottom of the crystal ; by transferring this to 

 a deeper receptacle, we can then dip up the diatoms with a pipette to 

 mount direct on slide or cover-glass. This method gives surprisingly 

 fine results," 



Colouring Bacteria.* — In a recent paper on this subject C. 

 Weigert (classifying Bacteria into Cocci and Bacilli, and the former 

 again into Micrococci and Megacocci) points out that two methods 

 are available for colouring these microganisms : — Istly, in clear 

 fluids, and in dried thin layers ; a method first employed by 

 Obermeyer for preserving bacteria in the case of Spirillum and 

 Spirochcete Ohermeyeri ; Koch being the first to colour preparations 

 dried in this way ; 2ndly, by sectional preparations hardened by 

 absolute alcohol. 



For most micrococci the nucleus colouring substance employed by 

 zoologists may be used ; as, for example, Schweiger-Seidel's modifica- 

 tion of carmine, aniline, or hfematoxylin. Micrococci are coloured 

 red by all nucleus colouring kinds of carmine, as purpurin, fuchsin, 

 and magdala : brown by Bismarck-brown and vesuvian ; brownish 

 violet by carmine, with subsequent washing of the preparation with 

 alcohol to which some ferric sesquichlorate has been added; green 

 by methyl-green : blue and violet by hematoxylin, iodine-violet, 

 methyl-violet, dahlia, and gentian-violet. All aniline colouring 

 matters are used by super-colouring the sections in strong aqueous 

 solutions, and then removing the colour either in acetic acid or in 

 alcohol, or in both, until the nucleus is difierentiated. 



For the larger Bacilli only the nucleus colouring aniline colour- 

 ing matters can be employed ; carmine and haematoxylin are useless 



* Arch. f. pathol. Anat. (Virchow), Ixxxviii. (1881) pp. 275-315. See Bot. 

 Centrabl, vi. (1881) p. 423. 



I 



