37 
Correspondence . 
sets the celloidin firmly. The objects are now enclosed in a thin, but 
very permeable film, so that they can be stained in liaematoxylin, car¬ 
mine, etc., aud in certain anilin stains such as safranin; the use of certain 
other anilin stains, such as gentian-violet, must be avoided, as they deeply 
deeply stain the celloidin film. The layer of celloidin becomes quite 
transparent in glycerine and Canada balsam, so there is no necessity for 
its removal. Both absolute alcohol and clove oil dissolve celloidin, so, if 
it is necessary to mount in balsam, the slide may be passed from 9o°/ 0 
alcohol to anilin oil, and then, preferably after washing in xylol, to Canada 
balsam. The great objection to this method is of course its complication, 
but by mounting in glycerine or glycerine jelly the trouble of clearing is 
done away with, though the preparation is not likely to be so permanent. 
I am, Sir, 
Yours, etc., 
Jan. 29th, 1902. V. H. Blackman. 
To the Bditor of “The New PhyToi.ogist.” 
Dkar Sir, 
One of the best methods of preparing unicellular organisms for 
microscopic examination is the following:—111 a small glass bottle of 
about one ounce capacity place half an ounce of i°/ 0 osmic acid or 
Flemming’s chromic acid mixture. By means of a pipette eject into it water 
containing the micro-organisms to be investigated. This may be continued 
until the solution is about half the original strength. Allow the organisms 
to remain in it for about one hour, until they have settled in a compact 
layer at the bottom of the bottle, then remove the fixing fluid; wash in 
water once or twice; add 30°/ 0 alcohol; replace this by 7o°/ 0 alcohol, aud, 
finally, preserve in methylated spirit. 
The organisms may be stained in .5% solution of Haematoxylin in 
distilled water. I11 order to do this, remove the methylated spirit; wash in 
water; soak for a short time in strong alum solution, then wash in distilled 
water, aud add the staining fluid. Allow this to act until the organisms 
appear deeply stained dark purple or black; remove the stain; wash in 
water and add again a strong solutiou of alum. In this the stain will be 
gradually washed out. Examine a few of the organisms from time to time 
under the microscope, and when sufficiently washed out, pour off the alum 
solution, and wash in water; add 70% alcohol, then methylated spirit, and 
finally replace by absolute alcohol. They should be thoroughly dehydrated 
by two or three changes of absolute alcohol, and, finally, this should be 
replaced by xylol. From the xylol the organism may be directly mounted 
in a solution of Canada balsam in x} r lol. 
This method is applicable to organisms which can be obtained in fairly 
large quantities at a time, such as Protococcus, Euglena, Desuiids, 
Diatoms, Volvox, Paramoecium, Astasia, Yeast, etc. It appears a com- 
plicated method 011 paper, but is really very simple in practice. 
Yours faithfully, 
H, W, 
Feb. 1st, 1902. 
