ScJiuette—Biochemical Study of Lake Mendota Plankton 599 
others. The Crustacea extracts deposited crystals of glycerides 
after standing for twelve hours. Viewed by polarized light 
between Nicol prisms under a magnification of 56 diameters, 
they showed a crystalline structure and when a selenite plate 
was interposed between the prisms, the characteristic play of 
colors was observed. 
The following analytical results were obtained: 
Sample 
Ether extract 
A 
9.88% 
B 
10.08 
C 
8.01 
D 
13.47 
E 
4.34 
154 
21.25 
5138 
7.611 
After standing over sulphuric acid for two months, the oils 
from the Daphnia and the Crustacea catches were examined for 
their physical and chemical constants. The nature of the 
residues found in the ether extracts from the plant catches 
made it inadvisable to attempt the determination of similar 
constants. The volatile acids, both water-soluble and water- 
insoluble as expressed by the Reichert-Meissl and Polenske 
numbers respectively, the iodine number according to the 
method of Hiibl, the saponification number and the index of 
refraction with the Abbe refractometer were determined. They 
are recorded in the following table. 
Sample C D 154 
I. R. at 25° C. 1.4777 1.4785 1.4810 
Iodine No. 102.08 87.58 172.88 
Saponification No. 248.60 208.56 
Reichert-Meissl No. _ 1.16 0.94 
Polenske No. 1.55 1.22 
Extraction with purified 95% alcohol of material which had 
been exhausted with ether showed that there is left much that 
is soluble in alcohol. Samples ‘"C,” ‘‘D” and ‘‘E” were first 
extracted quantitatively with anhydrous ether and then with 
alcohol. The amount of alcohol-soluble residue obtained by 
1 Determination by N. A. Bailey of the Survey. 
