CARBOHYDRATES, ACIDS, FATS, OILS 75 



be considered as complexes of the simple sugars already 

 described. Indeed, they make up the principal bulk of 

 the carbohydrate-content of cattle foods. These poly- 

 saccharides may be divided into three subgroups: the 

 starch group, the gum and vegetable mucilage group, and 

 the cellulose group. 



102. The starches. Starch is a widely distributed and 

 abundant constitutent of vegetable tissue. Food plants, 

 especially those most 'used by the human family, contain 

 it in generous proportions, in some seeds as much as 60 or 

 70 per cent being present. Probably only water and cellu- 

 lose are more abundant in the vegetable world. 



Starch does not exist in solution in the sap, but is 

 found in the interior of plant cells in the form of minute 

 grains which have a shape, size, and structure character- 

 istic of the seed in which they are found. Potato starch 

 grains are large, about -3^0 inch in diameter, and are kid- 

 ney-shaped, while those of the wheat are smaller, about 

 ToVo inch in diameter, and resemble in outline a thick 

 burning-glass. Corn starch grains are angular, being 

 somewhat six-sided, and those of other seeds show marked 

 and specific characteristics. These differences in size 

 and shape furnish the most important means of detecting 

 adulterations of one ground grain with another, a method 

 much used in the inspection of human and cattle foods. 



Unless modified by some chemical change, starch is 

 not dissolved by water. The starch grains are not affected 

 at all by cold water, and, in hot water, at first only swell 

 and burst. Prolonged treatment with hot water causes a 

 chemical change to more soluble substances. For this 

 reason the simple leaching of a food material removes no 

 starch by solution. At the same time, the cooking of a 

 ground grain so breaks up and liberates the starch grains 



