ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 139 



colour being attacked, as might be expected, by the preserving 

 material. 



Preparing Bacillus tuberculosis.* — Prof. J. Brun proposes the 

 following " ameliorations " to Koch and Ehrlich's processes. 



1st. Not to coagulate the albumen by heat, avoiding desiccation 

 at more than 80° C. At 100° or 120° C the bacteria are contracted. 



2nd. To render the organic matter transparent by acetic acid : — 

 Concentrated nitric acid 5 parts,| glacial acetic acid 10 parts, water 

 65 parts. 



3rd. To neutralize the nitric acid which, remaining to a greater 

 or less extent in the organic layer, at length decolorizes the bacteria 

 and renders them invisible. For this purpose is to be used a con- 

 centrated aqueous solution of aniline which neutralizes all the acid 

 not removed by repeated washings. 



4:th. To avoid Canada balsam, the index of which (1 ' 53) is too 

 high, and to take a neutral liquid having the same index as the 

 albuminoid substances (1*87): — Very white gelatine 14 parts, 

 salicylic acid * 25, distilled water 88.J This has an index of 1 • 356 

 for the yellow rays. Castor-oil can also be used, though its index 

 is 1-46. 



It is better to leave the field uncoloured than to colour it an 

 orange-brown with vesuvine or other colouring matter, because the 

 blue of the bacteria is rendered fainter by the complementary orange 

 tint. 



Staining Bacteria.§ — Professor C. Weigert adopts two distinct 

 principles in the staining of bacteria for microscopical examination, 

 according as they occur on the one hand in clear liquids or dried 

 masses, or, on the other, in tissues of which, after hardening, sections 

 can be made. For most Micrococci all nucleus-staining substances 

 are suitable, viz. (red) all the modifications of carmine, also purpurin, 

 fuchsin, and Magdala-red ; (brown) Bismarck-brown, vesuvin ; (violet- 

 brown) carmine, the preparations being washed, after staining, in 

 alcohol, to which some chloride of iron has been added ; (green) 

 methyl-green ; (blue and violet) haematoxylin, iodine-violet, methyl- 

 violet, dahlia, gentian-violet. 



For staining Bacilli and the rare Megacocci, anilin colours are 

 alone recommended ; carmine and hsematoxylin produce no effect ; of 

 the anilin colours only those which stain nuclei, viz. the basic 

 compounds (e.g. Bismarck-brown, methyl-violet, methyl-green, saf- 

 franin, fuchsin, magdala, &c.) are applicable; gentian- violet appears 

 to be especially suitable ; the objection to methyl- violet and fuchsin 

 is that in decolorizing in order to leave only the nucleus stained, the 



* Bull. Soc. Beige Micr., viii. (1882) pp. clxix.-lxxvii. Journ. de Microgr., 

 vi. (1882) pp. 500-3. 



t 1° Bull. Soc. Beige Micr. this is given as 15 parts. 



% In Journ. de Micr. tLis formula is not given, but in place of it the follow- 

 ing, which in Bull. Soc. Beige Micr. is said not to preserve so well the colour 

 of the bacteria : — Glycerine 10, commercial glucose 40, camphorated alcohol 10, 

 water 140. The index is 1-37. 



§ Arch, pathol. Anat. (Virchow), Ixxxiv. (1881) pp. 275-91. 



