378 SOME ZOOLOGICAL METHODS. 



simultaneously by BRANDT (Verh. d. physiol. Ges. Berlin, 1878), 

 by CERTES (Soc. Zool., 25 janv., 1881), and by HENNEGDY (Soc. 

 philom., 12fev., 1881). 



CERTES found that living Infusoria stain, while continuing 

 in life for a certain time/ in weak solutions of cyanin, Bismarck 

 brown, dahlia, violet 5 B, chrysoidin, nigrosin, methylen blue, 

 malachite green, iodine green, and other tar colours, and hserna- 

 toxylin. The solutions should be made with the liquid that 

 constitutes the natural habitat of the organisms. They should 

 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 "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. 



752. PFITZNER'S Method (Morph. Jahrb., xi, 1885, p. 454). 

 For Opalina Pfitzner proceeds as follows : The animals are 

 got on to a slide in a drop of water and covered. A drop of 

 concentrated solution of picric acid is run in under the cover 

 and the whole is put away in a moist chamber for several days. 

 The preparation is then washed out with water and stained 

 for a day or more with alum carmine or for a few hours with 

 Delafield's hsematoxylin. The preparation is then well washed 

 out with water, dehydrated, cleared with clove oil followed by 

 xylol, and mounted in balsam. 



All the reagents employed must be very carefully run in 

 under the cover, by placing a drop at the edge of the cover 

 and allowing it to penetrate gradually ; the drops must not be 

 drawn in by means of blotting-paper applied at the other side 

 of the cover, as this occasions a too rapid change of liquids 

 and produces shrinkage or swelling in the Infusoria. The 

 water used for washing out the picric acid may, however, be 

 used in this way, and should be plentifully employed. 



753. KORSCHELT'S Methods (Zool Anz., 1882, p. 217). 

 Infusoria are fixed on the slide by means of a drop of 

 1 per cent, osmic acid placed at the edge of the cover and 



