ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
605 
picric acid, and gentian-violet. After removing the paraffin by means 
of xylol and the latter with alcohol, the preparation is to be immersed 
in the alcoholic Orth’s carmine for a quarter of an hour. After 
washing in water it is transferred for 6 seconds to the gentian-violet 
solution and then to the iodine solution. After decolorising in alcohol - 
aceton (1/3) the preparation is passed rapidly through the picric acid- 
alcohol, and having been dehydrated in absolute alcohol and cleared up 
in xylol is mounted in balsam. 
The direct method, while applicable to all micro-organisms, should 
be reserved for those decolorised by Ehrlich or Gram. The necessary 
reagents are : — Phenol-thionin (saturated solution of thionin in 50° 
alcohol, 10 ccm. ; phenol in H 2 0 1 per cent., 100 ccm.) ; phenol-gentian- 
violet ; alcoholic solution of eosin ; alcohol-aceton ; absolute alcohol ; 
ether-alcohol, equal volumes ; xylol and balsam. Thionin or “ violet de 
Lauth ” belongs to the same group as the methylen or toluidin blues, 
and owing to its slight solubility in absolute alcohol is especially suitable 
for staining organisms decolorised by Gram. 
For cover-glass preparations the thionin or gentian-violet solution 
may be used, and the eosin employed as a contrast stain in certain cases. 
For sections the thionin solutions should only be used. 
In conclusion, the author says that by adding eosin to Gram’s iodine 
a double staining is effected. Iodine, 1 grm. ; iodide of potassium, 
2 grm.; saturated solution of aqueous eosin in alcohol at 90°, 20 ccm. ; 
H 2 0, 200 ccm. 
Methyl-blue and Methylen-blue.* — What follows may be news to 
some of our readers. “ The names of these two substances resemble 
each other so closely as to cause a greal deal of confusion, especially 
when an effort is made to abbreviate. We have taken the trouble to 
get authoritative definitions of these two forms from E. Merck 
(Darmstadt and New York), and Dr. Griibler (Leipsic). 
Methyl-blue is the sodium salt of tri-phenyl-para-rosanilin-sulphonic 
acid. It is also known as methyl-blue, M.B.f., for cotton. It is a 
dark-blue powder, forming a blue solution in water, and is used mostly 
for histological work. 
Methylen-blue is a salt of tetra-methylthionin, the double chloride 
with zinc being the form usually met with, though a simple hydro- 
chlorate, free from zinc, is also in the market, and this is what is 
supplied when ‘chemically pure’ is specified. It is used principally 
for staining in microscopic work, a very extensive use being as a contrast 
or ground stain for tubercle bacillus, the latter being stained with fuchsin 
(magenta).” 
(5) Mounting-, including- Slides, Preservative Fluids, &c. 
Formol.t — M. B. Blanchard has a note on this fluid, of which we 
have heard so much of late. He has himself been using it for leeches. 
He finds that after a year there is but the faintest alteration in the 
delicate coloration of these worms. M. Joubin has preserved in it 
various Cephalopods, and they have retained the same appearance as 
they have in the living state. 
* Micr. Bulletin, xi. (1894) p. 17. 
t Bull. Soc. Zool. France, xx. (1895) p. 93. 
