ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
247 
Limpid Colourless Solution of Copal.* — Dissolve 1 part of gum 
camphor in 12 parts of sulphuric ether, and to the solution add 4 parts 
of gum copal. Allow to stand until the copal is thoroughly softened, 
then add 4 parts of absolute alcohol and 1/4 of a part of rectified 
turpentine oil, and shake well. Set aside for a few days, agitating 
occasionally the while ; in about a week the liquid will have^separated 
into two layers, the upper being a limpid colourless solution of copal. 
Decant or siphon off the upper layer, and then treat the residue with 
more alcohol and oil of turpentine to obtain another limpid layer, and 
so on. If the solution be too thin it can be easily thickened by evapora- 
tion. The liquid can be made to dry more slowly by the addition of a 
small amount of Canada balsam. 
C6) Miscellaneous. 
Sources of Error in the Plankton Method. f — Mr. C. A. Kofoid has 
determined that the ordinary method of collecting plankton by drawing 
a net made of silk bolting cloth vertically through the water is subject 
to error, owing to the leakage of organisms through the openings in 
the silk. The leakage has hitherto been minimised or ignored, and the 
author has made experiments to ascertain the amount of the escape. 
The leakage has been tested by means of the Sedg wick-Rafter sand- 
filter ; by hard pressed filter-paper ; by the centrifuge ; and by the 
Berkefeld filter. 
It was found that in a general way the order given is that of increasing 
efficiency. The silk retains from 5 per cent, to less than 0 • 1 per cent, 
of the total number of the organisms present (excluding bacteria), as 
contrasted with the catch of the Berkefeld filter. Examination of the 
sand filtrate showed that 40 per cent, to 65 per cent, of the organisms 
present were captured, while the filter-paper method yielded 75 per cent, 
to 85 per cent, of the planktons. By the aid of the centrifuge 98 per 
cent, were sometimes captured. The Berkefeld filter method was found 
to be very satisfactory as far as the catch was concerned, but subject 
to a serious drawback, viz. the presence in considerable amount of 
infusorial earth, owing to the softness of the filter. 
Method of Demonstrating Assimilation.^ — Prof. F. Darwin has 
adopted the following modification of Farmer’s method for demon- 
strating assimilation in green leaves, A leaf of Elodea canadensis is 
mounted in water, and the preparation sealed by carefully ringing it 
with “wax-mixture” (15 parts resin, 50 parts vaseline, 35 parts bees- 
wax). The preparation is then placed in the dark, and the observer 
waits until the available oxygen has been absorbed and the circulation 
has come to rest, which takes place in from 3 to 6 hours. It is easy to 
show that the cessation of circulation is due to want of oxygen, by lifting 
the cover-glass with a needle and adding a drop of fresh water, when 
the protoplasm will begin to stream in a few minutes. 
Logarithmic Plotting of Biological Data.§ — Mr. D. J. Scourfield 
suggests that for plotting certain classes of data, such as those connected 
* National Druggist, xxvii. (1897) p. 371. 
t Science, vi. (1897) pp. 829-32. 
j Proc. Cambridge Phil. Soc., ix. (1898) pp. 338-40. 
§ Journ. Quekett Micr. Club, vi. (1897) pp. 419-23 (1 pi.). 
