ORGANIC CONTENT OF LAKE WATER 
199 
Table 9 brings together the facts for those residues for which the fats have been 
determined as ether extract. The table relates chiefly to Lake Mendota, there being 
samples from only two other lakes for comparison. 
The table gives the data and the results computed from them; the data include 
organic nitrogen, organic carbon, and ether extract; the computed results are crude 
protein, fats, and carbohydrates. To the fats is assigned a carbon content of 75 
per cent; the other substances are computed as in Table 8. Thus, in Table 9 the 
organic carbon is distributed to three classes of compounds. 
Table 9. — Total organic matter, ether extract included, milligrams per liter 
Lake 
Depth 
Date 
Total 
dry 
N 
C 
Ether 
extract 
Crude 
protein 
Fats 
Carbohy- 
drates 
Total 
0 
167. 8 
0. 567 
(l) 
0. 323 
3. 54 
0. 32 
(i) 
Do 
0 
169.0 
.307 
5. 58 
.380 
1.92 
.38 
9. 44 
11.74 
Do 
20 
Sept. 26, 1922. . 
162. 8 
.304 
4. 69 
.488 
1. 90 
.49 
7. 38 
9. 77 
Do 
20 
June 25, 1924 
172. 1 
.357 
6. 88 
.688 
2.23 
.69 
11. 51 
14.43 
Do 
0 
164. 3 
. 457 
5. 98 
. 482 
2. 86 
.48 
9. 09 
12. 43 
Do 
20 
6 samples 
149.7 
.452 
6. 35 
.765 
2.83 
.76 
9. 50 
13. 09 
Mean of 20_ 
.441 
6.06 
.564 
2.76 
.56 
9. 27 
12.59 
Geneva 
0 
July 16, 1923 
114.0 
.337 
4. 52 
. 217 
2. 11 
.34 
7. 00 
9. 45 
Green 
0 
July 18, 1923 
143.7 
.310 
3. 95 
.352 
1.94 
.31 
5. 98 
8.23 
1 Not determined. 
Table 10.— Percentile distribution of dissolved organic matter 
Lake 
Protein 
Fat 
Carbohy- 
drates 
Mendota: 
Surface (10 samples) 
23.0 
3.9 
73. 1 
Bottom (6 samples) 
21.7 
5.8 
72.5 
Mean (20 samples) 
21.9 
4.4 
73.7 
Green (1 sample) 
22.3 
3.6 
74. 1 
Geneva (1 sample) _ 
23.6 
3.8 
72.6 
The data from Lake Mendota comprise 20 samples and are numerous enough to 
warrant computing an average result. The results from Green Lake and Geneva 
show that the variation in the fats of different lakes is entirely similar to that in 
proteins and carbohydrates. The data from Lake Mendota, both in the single and 
the composite samples, show that there is a larger amount of fat in the water at the 
bottom than at the surface. It should be noticed that all of the single observations 
were made under summer conditions. The specimens that made up the composite 
surface sample were fairly distributed through the year; but all except one of the 
specimens from the bottom were taken during the period of the summer stratification 
of the water, when there would naturally be a maximum difference between surface 
and bottom. 
There is a very close correspondence between the average results of the 20 speci- 
mens from Lake Mendota reported in Table 9 and the mean of the 14 specimens 
reported in Table 8. If the organic matter for Table 9 is computed on the same 
basis as in Table 8, the result will be as follows: Nitrogenous, 2.76 milligrams per 
liter; nonnitrogenous, 10.21 milligrams; total, 12.97 milligrams. The total exceeds 
that of Table 9 by 0.38 milligram. The per cent of protein, when computed from 
