ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
713 
hinder hemisphere of the eye, after removal of the vitreous humour, is 
immersed in the ordinary osmio-bichromic mixture (bichromate of 
potash 3 per cent., 20 parts ; 1 per cent, solution of osmic acid, 5 or G 
parts). After being for one or two days in the mixture, the mass of 
liquid is drawn off from the parts, which are then put for twenty-four 
hours in a O' 75 or 1 per cent, solution of crystallized nitrate of silver. 
Without any washing the parts are returned to the osmio-bichromic 
mixture, care being taken that there is proportionately too much osmic 
acid. For a day at least the parts are again placed in the silver solution. 
For a few minutes they are then put into 40 per cent, alcohol, loosely 
imbedded in paraffin and cut into thick slices. After an hour’s washing 
with alcohol they are cleared and mounted. 
(5) Mounting:, including- Slides, Preservative Fluids, &c. 
Gum Thus.* — Dr. A. M. Edwards writes: — “I had supposed that 
Gum Thus was procurable in England as well as in the United States ; 
but it is not, as I learn from an inquiry in your December number. It 
is Gum Thus or Frankincense, and is got here from the tree of the pine. 
I procured it from the L. R. Barnard Chemical Company, dealers in dye- 
stuffs, chemicals, acids, oils, &c., at 58, Market Street, Newark, N.Y., 
U.S.A. I dissolve in commercial alcohol, with moderate heat, and then 
pour it off from the sediment. To this, three parts, I add one part of 
oil of cinnamon. It is used like Canada balsam, but dissolves in weak 
ammonia, alkali, carbonate of ammonia, soda or potash or borax. These 
can be used to clean the slides from superabundant medium. Those 
who have tried it, speak in flattering terms of it. It is of a high refrac- 
tive index, makes diatoms come out well with an ordinary one-fifth, and 
resolves the AmjpJiipleura pellucida with a 1/12 immersion. The colour, 
lightish-brown, is in the way, but I will bleach it by-and-by. Chlorine 
does not bleach it well. Try it, is all I say.” 
Pneumatic Bubble-remover.t— Mr. A. P. Weaver writes as fol- 
lows: — “Being annoyed with air-bubbles in my mounts, I have made 
a simple air-pump for removing them, as follows : — Take a small rubber 
syringe, the packing on the cylinder of which ought to be adjustable so 
as to fit the body of the syringe rather tightly ; cut off the nozzle rather 
close to the body, and bore a hole 3 mm. in diameter near the top of the 
latter, so that the packing will always be below the hole. Cut from an 
old rubber boot two washers 2 5 cm. in diameter, and with a central 
aperture of 2 cm. ; cement these washers together with Red Cross cement 
(such as is used for mending punctures in pneumatic bicycle tyres) ; 
cut from the boot two more washers of the same outside diameter and 
with a central hole a little wider than the nozzle of the syringe ; cement 
these last two washers together also, and cement them to the first two 
prepared ; you will now have a shallow chamber a little larger than the 
cover-glass. Force the nozzle of the syringe through the opening in the 
two plates and firmly cement it there. All these joints must be air-tight. 
To use the instrument, place the slide on a smooth surface, wet the 
under surface of the rubber washers and apply the same to the slide 
* Science Gossip, 1893, p. 68. + Amer. Mon. Micr. Journ., xiv. (1893) p. 126. 
