44 
The edges of the glass are ground by rub- 
bing upon a sheet of carborundum paper 
moistened with turpentine, or upon a metal or 
glass plate fed with carborundum and turpen- 
tine or water. 
It will be found convenient to have a dozen 
or two pockets—as many as are likely to be 
used in a single lecture, and to letter them 
consecutively on the thumb labels. A large 
collection of slides will take up very little 
room and will weigh very little. To avoid 
seratching, it is well to keep adjacent slides 
separated by sheets of paper of the same size. 
Before a lecture one merely arranges the 
empty pockets in the order of their letters and 
inserts the slides in the order in which they 
are to be shown. ArtTHuR W. Gray 
' Puysican Researce LABORATORY, 
Tue L. D. CauLK CoMPANY, 
MinrorD, DELAWARE, 
April 5, 1918 
WASHING MICROSCOPIC ORGANISMS 
One of the big hindrances to the study of 
plankton organisms is the difficulty encoun- 
tered in manipulating these microscopic plants 
and animals during the first few steps of the 
technique. Hall (Bot. Gaz., May, 1917) has 
outlined a method that the present writer has 
used for some years while at Cornell Univer- 
sity. The problem of thoroughly and easily 
washing plankton material was one of the big 
features with which to contend. 
For both diatoms and fresh-water crustacea 
the following procedure was found to be effi- 
cient: ! 
1. Kill and fix the material in a mixture of 
Chromic acid ....one part, 
Acetic acid ...... one half part, 
Distilled water ...four hundred parts. 
2. Wash by filtering through funnel. 
‘ 3. Mordant in one quarter per cent. ferric alum 
for thirty minutes. 
4, Wash again in funnel. 
5. Stain in one half per cent. hemotoxylin for two 
hours. 
6. Destain and wash as above. 
7. Dehydrate by the glycerine method and mount, 
or 
&. Dehydrate by the glycerine method and wash 
with 95 per cent. alcohol. 
SCIENCE 
[N. S. Vou. XLVIII. No. 1228 
9. Ten per cent. Venetian turpentine, concentrate 
and mount. 
The process of washing, originally, was to 
allow water to drip on the material that was 
held in a filter paper in a funnel. This may 
Kucakts ath 
seem an easy matter. However, several things 
have to be taken into account. Ohief among 
these is to maintain a constant flow of water 
during the process. Frequently a prolonged 
