ZOOLOGY AND BOTANY, MICROSCOPY^ ETC. 
259 
In order to examine specimens just mounted with an immersion lens, 
the author mentions the following device for preventing the cover-glass 
from slipping. A couple of needles, made hot, are laid along two sides 
of the cover-glass. This causes the resin to thicken from evaporation 
of the solvent. Of course, all the four sides might be banked up in this 
way, and the device is quite suitable for similar conditions of balsam or 
dammar. 
Fixatives for Diatom Preparations.^ — Herr E. Debes, after alluding 
to the isobutyl-alcoholic solution of shellac introduced by Dr. Witt, and 
which, though eminently suitable for a mounting medium, is equally 
difficult to make, proceeds to discuss two kinds of media convenient for 
mounting diatoms. These are resinous and gelatinous preparations. 
The resins are certain copals, and these are divisible into three classes 
according to their solvency in turpentine. To the first class, which is 
quite insoluble, belongs Zanzibar copal ; to the second, Manila or 
soft copal — this is only imperfectly soluble ; the third class includes 
those resins which, being quite soluble, are omitted. 
The Zanzibar, or insoluble copal is made into solution with isobutyl- 
alcohol, after having been previously treated with turpentine to dissolve 
out any resinous matter that may be present. The filtrate is then 
dissolved in isobutyl-alcohol and again filtered. The solution is quite 
colourless and clear, and is at once ready for use. 
The diatoms are fixed by placing on a 3-mm. cover-glass a small 
drop of the liquid, which spreads itself out all over the cover. The 
cover-glass is then put on a metal plate, heated by a spirit-lamp, and 
when the proper degree is arrived at, the diatoms are arranged. This 
degree is estimated by placing close to the cover-glass a small fragment 
of resin on a bit of cover-glass, and when the fragment is quite dissolved 
the correct degree of heat is indicated and the source of heat removed. 
Another way of estimating the proper amount of heat is to place a 
small strip of white writing-paper on the hot plate, and when this turns 
colour (white to yellow or brown), the source of heat is removed. After 
having been heated, both these resins (Manila and Zanzibar) become 
less soluble, an inconvenience which, as may be understood, may cause 
disasters if not properly anticipated. 
The gelatinous media are made from gelatin or isinglass. Two grm. 
of pure white gelatin are dissolved in 70 ccm. of glacial acetic acid (or 
3 grm. of isinglass in 75 ccm.), the mixture being placed in a well- 
stoppered bottle. By frequent shaking, the solution is efiected in three 
or four days. The process may be hastened by heating in a water-bath. 
If isinglass bo used the solution must be filtered to get rid of fat and 
fibres. Five grm. of the solution are then diluted with a mixture of 
3 grm. of ethyl-alcohol and 1*5 grm. isobutyl-alcohol. The mixture is 
made by squirting in small quantities of the latter through a pipette, and 
constantly shaking. If a cloudy or opalescent precipitate be formed, a 
little more acetic acid must be added. 
The solution must be put in a well-stoppered bottle and kept in a 
cool dark place. The fluid, which keeps well, is put on the cover-glass 
&c., with a pipette ; a small drop runs out peripherally to form a thin 
Zeitsclir. f. Wiss. Mikr., vi. (1889) pp. 283-92. 
