Schuette—-Biochemical Study of Lake Mendota Plankton 611 
The residues were then washed from the filters with 100 cc. 
of ten per cent hydlocMorie acidj the acid saturated with potas¬ 
sium chlorate crystals^ and the beakers allowed to stand for 
twenty-five days. Within twenty-four hours the residues had 
turned white. At the end of this period the solutions were 
diluted to about 700 ce. with distilled water^ the contents of the 
beakers filtered^ and thoroughly washed. To remove the 
last traces of chlorine and hydrochloric acid, the residues were 
macerated for twenty-four hours with 500 cc. of 0.05 normal 
ammonium hydroxide. The residues had lost their original 
texture and filtered very slowly. An operation that ordin¬ 
arily required thirty minutes at the most now took a week 
though filtered at the suction pump. The residues were col¬ 
lected on tared filter papers, washed with boiling water, and 
then with alcohol and ether. They were finally dried at the 
temperature of boiling water. 
The residues were hard and brittle. They contained no 
sulphur or phosphorus and it did not respond to the biuret or 
to the xanthoproteic reactions. This indicated the absence 
of a protein. Chitin was identified in these residues by 
Zander’s test^. This test depends upon the brown colora¬ 
tion obtained when chitin-containing substances are treated 
with a drop of a strong potassium iodide solution and then a 
concentrated zinc chloride solution. 
As in the ease of the crude fiber, these residues were found 
to contain nitrogen and in fact in the proportion in which ni¬ 
trogen has been reported in chitin by various investigators. 
While the values obtained were within the range of nitrogen 
reported by others, still the method leaves much to be desired 
both as to convenience and rapidity and because of the difficulty 
of obtaining a perfectly pure product. We believe that this form 
of nitrogen can be most expeditiously determined in the crude 
fiber. 
The Crustacea plankton only were examined for chitin. The 
extracts obtained in the initial stages of the analysis of catch 
were of such a slimy character that they were attacked 
by a mold before they had finally passed through the filter, 
and hence were discarded. The results follow: 
iPfluger’s Archiv 66^ 545. 
