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BULLETIN OE THE BUREAU OF FISHERIES 
The residues from large samples of evaporated water, from which the plankton has 
been extracted, yield an average of about 0.393 milligram per liter of organic nitrogen 
and about 5.80 milligrams of organic carbon. The nitrogen and carbon from the 
residues are called “dissolved.” (See Table 2.) 
2. The residues from the water of Lake Mendota yield ether extract to an 
average amount of more than one-half milligram per liter of water (0.564 milligram, 
Table 5). Green Lake and Lake Geneva yield comparable though smaller quantities. 
3. Part of the organic matter in the residues is, no doubt, particulate, but most 
of it seems to be dissolved. The quantitative relation of these two classes needs 
further investigation. 
4. The crude protein of the residues may be computed from the nitrogen (factor 
6.25), and the organic carbon may be distributed to proteins (assigning them 53 per 
cent C) and to nonnitrogenous matter (computed as 45 per cent C); if the ether 
extract has been determined the nonnitrogenous matter may be divided into fats 
(75 per cent C) and carbohydrates (45 per cent C). The average difference between 
these two methods of computation is about 3 per cent of the total organic matter. 
(See Tables 8 and 9.) 
5. On the first basis of computation the water of Lake Mendota contains an 
average of nearly 14 milligrams per liter of organic matter, of which about one-tenth 
is in the plankton. On the second basis, and employing for the plankton the larger 
average results of the plankton report, the total is nearly 15 milligrams per liter 
of water, of which less than 2 milligrams are in the plankton. (Tables 8 and 11.) 
6. The average nitrogen-carbon ratio in the plankton is about 1 to 6; in the 
dissolved matter it is about 1 to 14 or 15. In both cases the figures are subject 
to much variation. 
7. The average dissolved protein is from three to six times as great as that of the 
plankton; the dissolved nonnitrogenous material is about 10 times as great. (See 
Tables 8 and 11.) 
8. Studies of residues from 12 other lakes and 2 rivers show conditions essentially 
similar to those of Mendota, both in regard to plankton and dissolved organic matter. 
(See the several tables.) 
9. The question of the fundamental food supply of the lake must be reexamined 
in view of the presence of these relatively large amounts of dissolved organic matter. 
BIBLIOGRAPHY 
Birge, Edward A., and Chancey Juday. 
1922. The inland lakes of Wisconsin. The plankton. I. Its quantity and chemical com- 
position. Wisconsin Geological and Natural History Survey, Bulletin No. 64, 
Scientific Series No. 13, ix+222 pp., 40 text figs. Madison, Wis. 
Dohogalla, B. P., Chancey Juday, and W. H. Peterson. 
1925. The forms of nitrogen found in certain lake waters. Journal of Biological Chemistry, 
Vol. LXIII, No. 2, March, 1925, pp. 269-285, 4 text figs. Baltimore. 
Domogalla, B. P., E. B. Fred, and W. H. Peterson. 
1926. Seasonal variations in the ammonia and nitrate content of lake waters. Journal, 
American Water Works Association, vol. 15, No. 4, April, 1926, pp. 369-385, 4 text 
figs. Baltimore. 
