150 COMPOSITION OF THE BODY 



nary tissues of plants offer some resistance to hydrolysis, but' the 

 cellulose which is stored in the endosperm of seeds is capable of 

 being decomposed by acids with the formation of carbohydrates of 

 relatively low molecular weight. Thus carbohydrates are plastic 

 substances capable of being transformed from monosaccharids to 

 disaccharids and polysaccharids and vice versa. As these changes 

 are continually going on in the natural processes of metabolism, 

 the analysis of any plant would probably reveal carbohydrates 

 of different degrees of complexity. The sugars commonly occur 

 in solution in the sap of various plants, although they may some- 

 times be found in crystalline form, as in certain sacchariferous 

 seeds. The starches are found most abundantly in 

 tubers, roots and seeds, while the celluloses, pentosans, 

 lignoses, etc., form the principal part of the framework 

 of the plant. 



221, Fractional Extractions. The following extrac- 

 tions make a preliminary separation of the carbohy- 

 drates into groups, and separate them from other 

 matter in such manner as to leave them free for de- 

 termination or estimation. The material should be 

 very finely divided and air-dried. 



I. EXTRACTION WITH BENZINE. Extraction with 

 benzine removes the oils, fats, resins, pigments, etc. 

 The operation should be made at the boiling point 

 (not above 75 C.) over a steam bath and away from 

 FIG gi a flame. The Soxhlet apparatus is by far the best 

 Soxhlet'sap- an< ^ most economical for the purpose. When nothing 

 paratus for further can be extracted by a fresh quantity of the 

 on solvent, the extraction may be considered complete, 

 and alcohol When ^ s 1S accomplished the residue should be dried 



at 1 00 C. and weighed. 



II. EXTRACTION WITH ALCOHOL. The dry residue from I. 

 should next be extracted in the same manner with boiling alcohol 

 of 0.85 sp. gr. This process removes tannins, glucosides and part 

 of the sugars. 



