Schuette^Biochemical Study of Lake Mendota Plankton 613 
that the animal matter present can be neglected showed the 
presence of reducing sugars soluble in 50 per cent alcohol. A 
catch of blue-green algae and a mixture of diatoms and 
Crustacea were found to contain carbohydrates soluble in hot 
water. No pentoses were present although a qualitative test 
with Fehling’s solution indicated the presence of some reduc¬ 
ing sugars. An amorphous precipitate obtained in the puri¬ 
fied and concentrated aqueous extract of the diatom-crustacea 
catch with phenylhydrazine hydrochloride and sodium acetate 
did not show the presence of an osazone soluble in hot 60 per 
cent alcohol or in pyridine. A quantitative determination of 
the reducing power of this extract with Fehling’s solution both 
before and after hydrolysis with hydrochloric acid proved the 
absence of disaccharides or glucosides. 
No substance soluble in dilute sodium carbonate solution and 
comparable to the algin reported in marine algae is present 
in the catches examined. 
All the samples examined yielded measurable amounts of 
furfural which was collected as the phloroglucid and calculated 
to pentosan. It was found that the difference in the average 
yield of furfural obtained from a number of relatively pure 
vegetable catches and animal catches was not sufficiently great 
to warrant applying the determination of pentosans as a chemi¬ 
cal means of estimating the proportion of vegetable life in 
mixtures of animal and vegetable forms. 
The ether extracts of the Crustacea catches were found to 
be oils. The physical and chemical constants obtained indicate 
that they should be classed with the fish oils. The quantity 
and the physical nature of the extracts obtained from the 
vegetable catches did not permit of similar determinations. 
Note: The author wishes to extend his thanks to Dr. E. A. Birge, Dean of the College 
of Letters and Science of the University of Wisconsin and Director of the Wisconsin 
Geological and Natural History Survey, for suggesting and making possible the study 
of the problem outlined above. Thanks are also due to Mr. Chaney Juday of the Survey 
staff for collecting the material used in this study and his interest in the work. To 
Ptof. Richard Fischer he is also indebted for his timely help and suggestions. 
