CELL-CONTENTS AND FORMS OF CELLS. 149 



with their ready separation. The process is therefore modified 

 by either allowing the cereals to ferment, whereby the gluten 

 is rendered soluble and easily removed, or the flour is made into 

 a dough which is kneaded over running water, whereby the starch 

 grains are separated. The starch is subsequently purified by 

 washing and settling. It is dried by gentle heat and assumes the 

 columnar structure as seen in the more or less irregular particles 

 in the commercial product. One hundred pounds of wheat yield 

 from 55 to 59 pounds of starch, the fermentation process giving a 

 larger amount. 



In the preparation of corn starch, a weak solution of sodium 

 hydrate is usually employed to facilitate the separation of the 

 starch. Sulphurous acid is also used. One hundred pounds of 

 corn yield 50 pounds of starch. 



Rice starch is prepared by either an alkaline process or by an 

 acid process similar to that used in the manufacture of corn 

 starch, hydrochloric acid being employed instead of sulphurous 

 acid. Rice yields a greater percentage of starch than any of the 

 other raw materials, 100 pounds of the grain giving 70 per cent, 

 of starch. 



Starch is used as a food and for various other industrial pur- 

 poses. The principal nutritive starches are sago, tapioca, and 

 corn. Maranta, or arrowroot starch, is largely employed in the 

 preparation of infant foods. Much of the dextrin of commerce 

 is prepared by the action of dilute acids upon potato starch. 

 Starch for laundry purposes is prepared from wheat. Rice starch 

 is largely used as a dusting-powder. Cassava starch has consider- 

 able advantages over the other starches in the making of nitro- 

 compounds, and is employed in the preparation of smokeless 

 powders. 



PYRENOIDS. In the chromatophores of a number of algae a 

 distinct body is observed. It is more or less of a lenticular 

 shape, stained a dark purple on the addition of iodine, and is 

 known as a Pyrenoid. It is not definitely known whether it is 

 a true cell organ having a function similar to the plastids in 

 manufacturing starch or whether it is merely a mass of complex 

 reserve substances. It can be differentiated readily into two 

 distinct portions : an inner, somewhat highly refracting and 



