Schuette—Biochemical Study of Lake Mendota Plankton 597 
most abundant alga is Fragilaria. Daphnia constitutes by far 
the greater part of the material in sample “D,” a few cope- 
pods and very little plant material being present. Sample 
“ E’’consists almost entirely of two blue-green algae, viz., 
Aphanizomenon and Anabaena, which were found floating near 
the shore of the lake. Sample 154 consists of Daphnia pulex. 
Sample 5138 is not very different biologically from samples 
‘‘A’^ and ‘‘B.” The chief plant constitutent is Fragilaria 
while Daphnia is the chief animal constituent. It was not 
subjected to the same analyses and examination as the other 
catches of this series. It was particularly examined for the 
presence of carbohydrates. 
Our method of preparing the samples for analyses was to 
evaporate them in shallow dishes on a water-bath, kept below 
60°C., almost to dryness and to finish the operation in a vacuum 
oven at 65° C. over calcium chloride. Drying was complete 
in about 72 hours from the time that the samples reached the 
laboratory. The resulting residue could easily be ground in an 
ordinary meat grinder. The ground mass was then put through 
a small mesh sieve and the larger particles further comminuted 
in.an agate mortar. The dry weight of the catches follows: 
Sample 
A 
B 
C 
D 
E 
154 
5138 
Weight 
53 grams 
28 
187 “ 
160 ‘‘ 
470 ‘‘ 
92 ‘‘ 
125 
The dried plankton was rather hygroscopic, taking up about 
four per cent of moisture during the process of grinding. For 
this reason, all samples weighed out for analysis were again 
dried and the results calculated to a moisture-free basis. It was 
found by experiment that drying for twelve hours in an elec¬ 
tric oven kept at 60° C. was sufficient to bring the sample to 
constant weight. 
