ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
279 
in the crystalloids. M. Poulsen recommends also the two following 
processes : — 
(1) Very thin sections of the endosperm are first placed in absolute 
alcohol for twenty-four hours, and, as soon as they are hard, transferred 
for an hour to a 25 per cent, aqueous solution of tannic acid, and then 
washed with distilled water. They are then plunged in an aqueous 
solution of potassium bichromate until they become brown or yellow. 
The sections thus made are preserved in glycerin, and show the trans- 
parent aleurone-grains with great clearness. 
(2) After being hardened as before, the sections are made to imbibe 
tannin and washed ; they are then placed for an hour or less in a 10-20 
per cent, aqueous solution of iron sulphate, which brings out a very 
dark-blue or almost black colour. The sections are then washed and 
dehydrated in absolute alcohol; and the preparations thus made are 
placed first of all in essence of clove, and finally in Canada balsam. 
They are beautifully clear, and very durable. 
Reference Tables for Microscopical Work.* — The following con- 
tinues Prof. A. B. Aubert’s reference tables : f — 
Gum with chloral hydrate : — Gum arabic, chloral hydrate, water. A 
cylinder, 60 ccm. contents, is filled two-thirds with gum arabic in pieces ; 
to this is added a solution of chloral hydrate (several per cent.) con- 
taining 5-10 per cent, of glycerin; shake often ; in a few days the gum 
will dissolve ; the syrupy liquid is filtered. Carmine and hfematoxylin 
stained objects can be mounted in this medium. 
Gum and acetate of potash or of ammonia : — Gum arabic, acetate of 
potash or of ammonia, glycerin, water. Made as the preceding medium, 
only a solution of potassic or ammonic acetate is used instead of a solu- 
tion of chloral. Anilin-stained objects can be mounted in this. 
Iodized serum, artificial (Ranvier) : — (1) distilled water, 135 grm. ; 
(2) egg albumen, 15 grm.; (3) common salt, 0*2 grm.; (4) tincture 
of iodine, 3 grm. Mix 1, 2, and 3, and filter ; add 4, and filter again. 
Used for examinations, not for mounting. 
Potassio-mercuric iodide (Stephenson) ; — Biniodide of mercury, iodide 
of potassium, water. To the water add an excess of each salt, and filter. 
This gives a very dense liquid of high refractive index (3*02). For 
diatoms, &c., may be used diluted. 
Monobromide of naphthalin. — High refractive index ; for diatoms, &c. 
Monobromide balsam : — Solution of hardened Canada balsam in 
monobromide of naphthalin. Refractive index high, 1*6; shows finer 
structure of diatoms, &c. 
Monobromide tolu. Weir’s medium: — Solution of balsam tolu in 
monobromide of naphthalin. Refractive index, 1*73; may prove very 
valuable as a medium for diatoms. Preparation. — Dissolve 3 oz. of 
balsam of tolu in 4 fluid drams of benzol, add 4 fluid oz. carbon 
disulphide ; renew this treatment with more carbon disulphide ; pour 
it off again ; evaporate the benzol from the balsam tolu. The tolu will 
now be free from cinnamic acid ; put 1 fluid dram of monobromide of 
naphthalin in 1/2 oz. vial; add enough of the purified tolu to make a 
stiff mixture or solution when cold. Heat to 104° or 122° F. when using. 
Microscope, xi. (1891) pp. 12-14. 
f See ante , p. 142. 
