610 Wisconsin Academy of Sciences, Arts, and Letters. 
After this series of experiments had been completed we found 
that Krober and Eimbach^ had successfully applied the 
pentosan determination to a mathematical formula for deter¬ 
mining the percentage composition of paper made from a mix¬ 
ture of rag stock and wood pulp. They established an aver¬ 
age value of 12 per cent pentosans in wood pulp and an aver¬ 
age value of 1 per cent pentosans in the cellulose of rags^ etc. 
The large difference in values which they obtained with their 
material as compared with that obtained by us from the plank¬ 
ton samples is to be noted. 
CJiitin. The shells of the plankton Crustacea contain chitin, 
Gibson^ showed that it sometimes replaces cellulose in plants. 
Winterstein has isolated it from certain fungi®, as Boletus 
edulis, Polyporus officinalis, Agaricus compestris and others. 
Wester^ obtained it from the shell of the shrimp, from cantharis, 
champignon, ergot, the cuttlefish and from crabs ^ eyes. Hegler® 
and KohP report having found chitin in the walls of many blue- 
green algae but Wester was unable to confirm their results. 
With modifications to adapt it to our needs, we tried Win¬ 
terstein’s scheme of separation and isolation. The fat-free 
sample was boiled under a reflux condenser with three suc¬ 
cessive portions of 95 per cent alcohol, washed by decantation, 
and the filtrate and washings evaporated under reduced pres¬ 
sure to dryness. This residue was examined as above de¬ 
scribed for nitrogen. Extraction by 60 per cent alcohol fol¬ 
lowed'and the residue was washed with cold water until color¬ 
less. The filtrate was practically colorless which showed 
that the extraction with the strong alcohol is quantitative. 
Proteins were then decomposed by treating the residue with 
300 cc. of a one per cent sodium hydroxide solution. The so¬ 
lution was left standing in the cold for sixteen hours and was 
then boiled for thirty minutes. This digestion, after the 
alkali and the decomposition products had been washed out, 
was followed by a digestion in the cold for twenty-four hours 
with 200 cc. of 0.1 normal hydrochloric acid and then by di¬ 
gesting on the water-bath for four hours. The residue so ob¬ 
tained was washed with boiling water. 
iz. angew. Chem. 25, 510 (1902). 
^Ber, 28, 821 (1895). 
3Z. physiol. Chem. 1©, 521-630 (1894). 
^Arch. d. Fharm. 247, 282-307 (1909). 
®Jahrb. Wiss. Bot., 36, 279 (1901). 
®Ueber d. Organ, und Physiol. Cyanophyceenzelle, Jena, 1903. 
