42 PHYSIOLOGICAL CHEMISTRY. 



tose, and besides this they yield the ester derivatives charac- 

 teristic of polyhydric alcohols. In their natural condition they 

 are mostly insoluble in water and other solvents. It is cus- 

 tomary to make three classes of these compounds, of which 

 the starches or amyloses, as the most important, will be treated 

 first. 



The Amyloses. In the vegetable kingdom starch is a com- 

 mon and widely distributed reserve material, a sugar, probably 

 saccharose, being first formed as a synthetic product. Starch 



FIG. 3. Wheat starch magnified about 350 diameters. 



is found in many seeds, grains and tubers in the form of 

 minute granules which are often characteristic in shape or 

 size. They may be extremely small, pepper starch for ex- 

 ample, or relatively large, as in the case of arrowroot starch. 

 Under the microscope these granules often appear to be built 

 up of concentric layers, and furthermore they are not homo- 

 geneous in composition. The outer part of the granule con- 

 sists of a covering or sheath of starch cellulose within which 

 is the large mass of starch granulose. The cellulose sheath 



