612 Wisconsin Academy of Sciences, Arts, and Letters, 
Sample 
Residue 
4.41% 
4.45 
3.25 
Nitrogen in the residue 
A 
B 
154 
5.91% 
5.64 
6.21 
Summary 
In the examination of seven typical plankton catches made 
preliminary to and in part concomitant with an extensive 
chemical survey of the plankton of Lakes Mendota and Monona, 
it was found that from 40 to 87 per cent of the total nitrogen 
was present in an available form, that is as protein nitrogen. 
The remainder was non-protein nitrogen which included, among 
other forms, that nitrogen entering into the indigestible chitin 
molecule. The latter was present in larger amounts in those 
catches which contain a preponderance of animal matter 
(Crustacea) than in those catches which consist almost en¬ 
tirely of vegetable matter. Chitin was isolated from the 
Crustacea plankton in which it is present to the extent of 5.9 to 
6.2 per cent of the dry weight. 
Nitrogen of the mono-amino acids was the predominant 
form among the hydrolysis products with hydrochloric acid of 
both the plant and Crustacea catches. Amide-nitrogen, di-amino 
nitrogen and ‘‘humic” nitrogen made up the rest. The 
nitrogenous constituents of the alcoholic extracts of the 
Crustacea catches were almost all water-soluble. 
The sulphur content of all the catches examined in this con¬ 
nection and that of two other catches selected at random from 
the larger series of the survey showed a surprising constancy. 
This constancy was not shared, however, to such a marked de¬ 
gree by the phosphorus. 
An investigation as to the nature of the carbohydrates pres¬ 
ent was perforce only a preliminary survey in this direction. 
Qualitative tests indicated the presence of only small quanti¬ 
ties of sugars. The amounts detected made it apparent that a 
larger quantity of material would be necessary for a thorough 
study than was available with present means of collecting. 
The Crustacea catches did not show the presence of any re¬ 
ducing sugars either in the aqueous extract oi the extracts 
with 95 per cent, 70 per cent, or 50 per cent alcohol. Those 
catches in which plant matter predominates to such an extent 
