Jan. 1891.] BOTANICAL SOCIETY OF EDINBURGH. 47 



of an orange brick-red colour. My friend Mr Terras was 

 kind enough to test this heliocin chemically, and found it to 

 act thus : — 



The dye dissolves in concentrated snlphnric acid with a 

 red orange colour, which on boiling becomes dark brown. 

 Water added to the dark brown fluid does not produce any 

 precipitate. Hydrochloric acid added to the solution in 

 water gives no precipitate, and does not change the colour. 

 Zinc dust added to the acid solution decolorises it in the 

 cold easily, and the colour does not return on exposure to 

 the air. Strong caustic potash added to the watery solution 

 of the dye produces no chauge either in the cold or when 

 boiled. Zinc dust added to the alkaline solution decolorises 

 it in the cold. 



Besides the heliocin just described another one is in the 

 market, a dark brownish-red powder soluble in water, with a 

 distinct fluorescence, readily soluble in alcohol, and giving 

 the reactions of true eosins. 



One should endeavour to get the heliocin first described, 

 for it makes a beautiful contrast with the blue, and allows 

 one to study the finer structure of nucleoli. 



Should either of the two heliocins not be obtainable, any 

 of the eosins, or erythrosins, may be substituted, when treat- 

 ing: vegetable tissues, while for animal tissues safranin makes 

 a tolerably good substitute. 



Another differential stain is got by placing living tissues 

 for at least a week in a saturated picric acid solution of 

 absolute alcohol, to which that variety of nigrosine known as 

 alcohol-soluble ni2;rosine has been added. After-stainins; 

 the sections with eosin or Klein enberg's hsematoxylin causes 

 the nigrosine to be replaced by either dye leaving only the 

 nucleolus of a greeuish-blue colour. 



Dr Macfarlane remarked that Mr Mann's investigation 

 tended to confirm observations he had communicated to the 

 Society some years ago, in which he recorded the existence 

 of an endo-nucleolus as a constant body, and pointed out the 

 importance of the nucleolus itself as a definite and important 

 factor within the nucleus. His observations had been as yet 

 altogether passed over by workers, alike on the vegetable and 

 the animal side; but he still held the views he had formerly 



