194 
BULLETIN OF THE BUREAU OF FISHERIES 
In the case of the other lakes there is no such opportunity for comparison, as 
the analyses are not so numerous. In general, the cases reported are fairly repre- 
sentative. The total plankton reported from Lakes Kegonsa and Wingra is very 
large, aggregating more than 60 per cent of the total organic matter from the 14 
specimens. Large amounts, but less noticeable, also are found in Lake Monona 
and Lake Waubesa. In the first two cases the water was collected close to the 
j 
surface at the time of great growths of blue-green algse, and the collection was made 
at this time in order to note the effect of these growths on the dissolved organic 
matter. The samples from the other two lakes also were taken at a time of maximum 
abundance of plankton. It will be noted that the “ash” is relatively low in these 
specimens, especially in the first two cases. The ash of the blue-green algse is low; 
in 11 analyses (plankton report, p. 215) it ranged from 4.3 per cent to 7.8 per 
cent, and the presence of many milligrams per liter of this material greatly reduces 
the percentage of total inorganic matter. 
The ratio of the nitrogen to the total organic matter of the plankton in Lake 
Mendota is 1 to 20.1, a ratio that is much lower than the average for the catches 
analyzed in the plankton report. In these the ratio was 1 to 14.1. The ratio of the 
average from the other lakes, as given in Table 6, is 1 to 21.8, or 1 to 20.2 if Lakes 
Kengosa and Waubesa are omitted as being exceptional cases. I 
II. DISCUSSION OF THE DATA 
ORGANIC NITROGEN AND ORGANIC CARBON 
Table 2 states the amount of organic nitrogen and organic carbon found in the 
residues from the water of the several lakes. They represent what is usually called 
“dissolved” or “soluble” carbon or nitrogen, as the water has been passed through 
a supercentrifuge to remove the plankton. 
It should be noted that the lake water received a different treatment from that 
given to sea water by Raben (1910) and by Moore (Moore, et al., 1912); for exam- 
ple, in determining the dissolved carbon. In their experiments a small amount of 
water was employed, which had been passed through a Berkefeld filter. In studies 
on lake water the plankton was extracted from large quantities of water — 50 to 575 
liters — by means of the centrifuge. It is not probable that the two methods yield 
identical results. Both leave the water far from optically pure, and both undoubt- 
edly remove substances that are neither living cells nor organic debris that exists 
in a particulate form — to employ Moore’s useful word. In either case the weight 
of the matter left in particulate form probably is very small. 
Two classes of experiments were made in the course of our studies that give 
some idea of the percentage of the particulate organic matter that was removed by 
the centrifuge. The first gave an indirect answer, based on the percentage of bacteria 
removed from the water by the centrifuge. 
It is difficult to imagine that particles of organic debris suspended in water 
should be free from bacteria, and if they have bacteria adherent to them or colonized 
in them, a rough measure of the efficiency of any process in removing these particles 
of debris may be found in its efficiency in removing bacteria. 
