ScJiuette—Biochemical Study of Lake Mendota Plankton 605 
The residues obtained in quantitatively extracting five of the 
catches in this series with 95 per cent purified alcohol were 
found to be nitrogen-containing. The extracts were evapor¬ 
ated under diminished pressure and then dried over sulphuric 
acid. A quantitative extraction of the Daphnia catch was 
not made at this time^ but the alcoholic extract obtained in an 
attempt at the isolation of chitin was evaporated to dryness as 
above examined for nitrogen. The residues from the plant 
catches were of a gummy consistency. Their nature was such 
as to preclude grinding preparatory to taking a representative 
sample and hence the nitrogen was not determined. Inasmuch 
as the Crustacea catches contain approximately the same amount 
of alcohol-soluble matter, the latter was mixed and the nitrogen 
content of the mixture determined. Analyses show that prac¬ 
tically all of the nitrogen entering into the alcohol extract is 
water-soluble. The remainder is considered as “coagulable 
nitrogen’’ and proteose nitrogen. 
The results obtained are recorded below. 
Sample 
Alcohol 
extract 
Total 
nitrogen 
Water-soluble 
nitrogen 
A. 
28.65% 
29.71 
54.10 
53.83 
26.97 
B... 
C...... 
9.69% 
9.33% 
D. 
E... 
154... 
10.82 
10.55 
Carbohydrates. Various hexose and pentose sugars have been 
reported in the marine algae. Konig and Betties^ found 
d-galaetose, levulose and d-glucose. Muther and Tollens^ 
found d-galaetose, small quantities of arabinose and fucose. 
Kylin^ found traces of dextrose and trehalose. Brandt^ 
identified none of the carbohydrates in the plankton of the Bay 
of -Kiel although he reports their presence. He made an ele¬ 
mentary analysis, calculated the carbon and hydrogen to pro¬ 
tein and fat, and the remainder to carbohydrate. Hoagland® 
studying the organic constituents of the Pacific coast kelps re- 
1 Loc. cit. 
aBer. 37, 298-305 (1904). 
3Z. physiol. Chem. 94, 337-425 (1905). 
* Loc. cit. 
® Jc. Agr. Research 4, 337-425 (1915). 
