Schuette—Biochemical Study of Lake Mendota Plankton 609 
and accuracy. Although the organisms in each catch are 
counted under the microscope per unit volume, a check by 
chemical means is often desirable. 
The alleged absence of pentosans in the animal kingdom 
suggested the possibility of adapting the results of the pento¬ 
san determination of a plankton catch to an estimation of the 
proportion of vegetable life in a mixture of animal and vege¬ 
table forms. In order to do this, it is necessary to examine 
a number of pure representative vegetable samples for the pur¬ 
pose of establishing an average figure on the yield of furfural 
obtained under the conditions of the determination. Like¬ 
wise it is necessary to obtain an average figure for pure animal 
forms of the kind met with in a survey of this kind. 
The pentosan content of seven catches of the larger series 
which were known to be nearly pure Crustacea was determined. 
The quantity of pentosan-reacting material obtained and which 
was weighed as phloroglucid ranged from 0.67 to 1.32 per cent, 
or an average of 0.82 per cent of the dry weight. It was not 
of the same appearance, nor did it seem to have the same tex¬ 
ture, as the phloroglucid obtained from the vegetable samples 
examined. The average content of several nearly pure algal 
catches was found to be 1.40 per cent. Various mixtures of 
these catches were made and the pentosan content of the mix¬ 
ture determined. The values found in twelve mixtures all 
lay within a narrow range—0.65 to 1.35 per cent. The dif¬ 
ference in the average values found is apparently not great 
enough to cause an appreciable difference in the mixtures ex¬ 
amined. 
The following data are added to show the futility of trying 
to make a practical application of this determination. 
Algae 
Crustacea 
Pentosan 
obtained 
1 part....... 
1 part 
1 12% 
2 . 
1 
1.12 
3 “ . 
1 “ 
1.25 
4 “ 
1 “ 
1.26 
1 *• . 
2 “ 
1.23 
1 “ ... 
3 “ 
0.99 
1 “ ..... 
4 “ 
0.65 
5 “ . 
1 “ 
1.35 
5 “ . . 
3 “ 
1.01 
7 “ . 
1 “ 
1.20 
3 " .. 
5 ■* 
0.96 
39—S. A. L. 
