Nutrition Investigations. 309 



Qualitative tests for mannose have been made by Storer's (271) 

 method. The products of hydrolysis, freed from the greater part of 

 the salts, gums, etc., in the manner already described, were taken 

 up in a little water, and portions of 1 cc. or 2 cc. placed in test 

 tubes. The reagent for testing was freshly prepared by shaking 

 together 1 cc. of phenylhydrazin, 2 cc. of glacial acetic acid, and 

 10 cc. of distilled water. 3-16 drops of this reagent were added to 

 each of the test tubes, and after standing several hours at room tem- 

 perature, they were examined for precipitates of mannose-hydrazone. 

 These precipitates were examined under the microscope, because they 

 usually contained considerable amorphous matter. The mannose- 

 hydrazone itself does not come down as colorless rhombic plates at 

 first, but as globules of greenish-yellow or brownish-yellow color, 

 sometimes smooth and resembling large yeast cells in the way they 

 c uster together, and at other times covered with blunt points or 

 spines. When these globules were observed, the precipitate was care- 

 fully washed with water, sometimes without removing from the test- 

 tube, the last drops being taken up with filter paper, and then dissolved 

 in warm diluted alcohol (3 parts of 95 per cent to 1 part water), which 

 was not filtered, but decanted from the amorphous insoluble portion, 

 and allowed to evaporate slowly to facilitate the formation of crys- 

 tals. Unless these crystals could be obtained, the tests were consid- 

 ered negative, although Storer has pointed out that they are sometimes 

 diflScult to obtain, even when true mannose-hydrazone balls are 

 present. 



All quantitative determinations have been made in duplicate un- 

 less otherwise stated. 



PENTOSAN PREPARATIONS. 



Dulse. 



A pure, water-soluble pentosan-preparation has been obtained from 

 dulse (Rhodymenia palmata). After boiling in water, in an open 

 vessel, with occasional stirring, for several hours, this dark, reddish- 

 brown seaweed yielded a carbohydrate, non-mucilaginous in character, 

 which could be precipitated from its solutions by alcohol. About 12 

 hours' boihng proved to be necessary for complete extractions. The 

 hot, brown, watery extract was first filtered through gauze, and then 

 through cotton, as it clogged up filter paper very quickly. This 

 filtrate, concentrated to a syrup on a water bath, was poured while 



