ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
G91 
though he repeatedly mentions the fact of the differentiation. I am un- 
able to follow him in his method, and, notwithstanding many trials, have 
failed to get his differential stain, namely, the chromatin-elements of the 
nucleus green and the nucleolus red by means of methyl-green and 
fuchsin. 
While endeavouring to stain the nucleolus and endo-nucleolus differ- 
entially, my attention was drawn by Dr. Macfarlane to heliocin as a 
good nuclear stain for Spirogyra. By extending its action in combina- 
tion with anilin-blue to other tissues, I have succeeded in obtaining an 
excellent differentiation. 
Method. — Tissues, both vegetable and animal, preferably fixed by my 
picro-corrosive method,* are treated for ten minutes in a saturated solu- 
tion of heliocin in 50 per cent, alcohol ; the sections are then transferred 
for from five to fifteen minutes to a saturated watery solution of anilin- 
blue. The superfluous stain is rapidly washed off by distilled water, 
and the sections placed again for one to two minutes in the heliocin- 
solution, dehydrated, cleared by resinified turpentine, and mounted in 
turpentine-balsam. 
Effect . — The whole of the cell and the nucleus blue, the nucleolus 
red. In karyokinetic figures the cell and nuclear barrel are stained 
blue, the nuclear plate, monaster and diasters stained red. I 
The chemical constitution of the heliocin I used I am unable to find 
out ; when dry it is a brick-red powder, readily soluble in water, slightly 
so in absolute alcohol, and in each case showing no fluorescence. A 
watery solution is 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 sulphuric 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 decolorizes 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 
change either in the cold or when boiled. Zinc-dust added to the 
alkaline solution decolorizes 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 treating vegetable 
tissues, while for animal tissues safranin makes a tolerably good sub- 
stitute. 
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 
* See Trans. Bot. Soc. Edinb., xviii. (1890) p. 432, et supra , pp. 686 et seq. 
f “I may state that in dividing cells of the root of Nymphsea alba , wo may stain 
the whole of the cell pink, and the nuclear plate, monasters and diasters blue, by 
treating sections first with alcoholic eosin and then with alcoholic methylene- blue.” 
