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BULLETIN OF THE BUREAU OF FISHERIES 
So far as the dissolved organic matter is concerned, much the same comment 
may be made on Table 8 as on Table 2, from which it is derived. The total quan- 
tity of dissolved organic matter varies greatly in different lakes and in the same lake 
at different times. It may be less than 7 milligrams per liter (Devils Lake), or it 
may be more than 28 milligrams (Turtle Lake) — a fourfold range. The second 
observation on Green Lake was nearly 70 per cent larger than the first; and in the 
14 observations on Lake Mendota the smallest quantity is less than one-half of the 
largest. These results are entirely in accord with those on the plankton, though 
the range of variation is much smaller. 
There is much difference in the relation of nitrogenous to nonnitrogenous matter, 
just as there is in the nitrogen-carbon ratio of Table 2; and, as in that case, the 
average relation is much the same in the various groups. In the 14 cases from Lake 
Mendota the crude protein ranges from 12.6 to 36.9 per cent, a nearly threefold 
range; in the 14 cases from other lakes the minimum percentage is 10.6 per cent 
in Turtle Lake and the maximum is 29.5 per cent in Lake Kegonsa. The average 
per cent for Lake Mendota is 19.6; for the other lakes it is 20.1. This average is 
lower than it is in the plankton. Table 8 shows that in Lake Mendota the crude 
protein is 33.1 per cent of the total organic matter of the plankton; in the other 
lakes it is 31.1 per cent. The plankton report (p. 196) gives 44.5 per cent as the 
average for Lake Mendota during the years when that study was made. 
The total organic matter of the water is obtained by adding the plankton and 
the dissolved matter, as is done in Table 8. In interpreting these figures the state- 
ment that was made earlier in this paper should be remembered. Not everything 
included under the first head is properly plankton, and the amount of nonplankton 
organic matter there included will increase with the efficiency of the centrifuging 
process. It is true, also, that not all of the “dissolved” matter really is dissolved. 
These divisions of the organic content of the lake water overlap to some extent, the 
degree of overlapping being dependent on the efficiency of the processes of separa- 
tion. But, on the whole, the two categories fairly represent the facts. 
The quantitative relation between plankton and dissolved organic matter is 
very variable. In the case of Lake Mendota the plankton may constitute nearly 
one-fifth of the total organic matter, or it may be less than one-sixteenth; in the 
other lakes the range is much greater. The plankton is more than one-half the 
total organic matter in Lake Kegonsa; nearly one-half in Wingra; and it is as little 
as one-fortieth of the total in Turtle Lake. 
The mean of the 14 specimens from Lake Mendota shows that the crude pro- 
tein of the plankton constitutes about one-sixth of the total protein, and the non- 
nitrogenous part of the plankton is little more than one-twelfth of the corresponding 
total. The range of variation in other lakes is so great in comparison to the number 
of observations that an average result has not much value. 
TOTAL ORGANIC MATTER, INCLUDING FATS 
In this discussion the ether extract is regarded as fat. The quantities obtained 
were too small for further chemical treatment, but under the microscope they appeared 
as transparent droplets of fat. 
