PRESERVING 1NFUSOKIA. 463 



be very weak, that is, of strengths varying between 1 : 10,000 

 and 1 : 100,000. For cyanin, 1 : 500,000 is strong enough. 



The " nucleus " may be stained in the living organism by 

 dahlia and malachite green. Bismarck brown only colours 

 the (t nucleus " of certain species (Nychtoterus, Opalina HEN- 

 NEGUY). The "nucleus" frequently behaves differently in 

 allied species. 



A double stain of the nucleus (green) and protoplasm 

 (violet) may be obtained by the simultaneous employment of 

 dahlia and malachite green. 



Examination in a coloured medium in which the organisms 

 do not stain, but show up on a coloured background in a 

 manner that produces somewhat the effect of dark-ground 

 illumination, is sometimes helpful. CEETES (Bull. Soc. Zool. 

 de France, xiii, 1888, p. 230) recommends solution of anilin 

 black for this purpose ; Infusoria will live in it for weeks. 

 FABEE-DOMEEGUE (Ann. de Microgr., ii, 1889, p. 545 ; Journ. 

 Roy. Mic. Soc., 1889, p. 832) recommends concentrated solu- 

 tion of diphenylamin blue. 



859. Fixing and Preserving. PPITZNEE (Morph. Jahrb., xi, 

 1885, p. 454) used concentrated solution of picric acid run in 

 under the cover. 



BLANC (Zool. Anz., 1882, p. 22) advises liquid of Kleinen- 

 berg diluted with about a volume of water, and acidified 

 with acetic acid. 



KOESCHELT (Zool. Anz., 1882, p. 217) recommends 1 per 

 cent, osmic acid, or for Amoebae, 2 per cent, chromic acid. 



LANSBEEG (ibid., p. 336) advises the same reagents, but 

 recommends bringing the organisms into the fixing liquid 

 with a pipette, instead of running in the fixing liquid under 

 the cover. 



CATTANEO'S Methods (Bollettino Scientifico, iii and iv; Journ. 

 Roy. Mic. Soc., 1885, p. 538) are as follows : Fix for a few 

 minutes with -J- per cent, aqueous solution of chloride of palla- 

 dium. This is the best fixing agent, as it hardens in a few 

 minutes without blackening the structures. Double chloride 

 of gold and cadmium also fixes well, and brings out nuclei 

 even better than the palladium. Solution of iodide of mercury 

 and potash (J per cent.) is useful for bringing out proto- 

 plasmic networks, as it stains the granules of 



