MICROSCOPY OF THE COMMON STARCHES. 61 
until the seventeenth century that the potato was used as 
a source of carbohydrate; and corn-starch is of course a 
still more recent product. These three are by far the 
most important of the starches. As might be inferred 
from the scale of prices given above, corn-starch is used 
for most purposes, the amount produced in the United 
States in 1903 being probably in the neighborhood of 
75,000 tons. Potato-starch ranks next with a produc- 
tion of 16,000 tons in 1903, and the amount of wheat- 
starch was perhaps 10,000 tons. 
The purposes for which this great supply is intended 
may be grouped roughly under four heads: starch is 
used for a food material, for stiffening and sizing, as a 
powder, or as a raw material for the manufacture of 
other substances. Mixed with nitrogenous bodies, in 
the form of flour, its supreme importance is of course as a 
nutritive substance; and even the purified product, in the 
case of corn-starch, forms no insignificant contribution to 
our dietary. The sago and tapioca flours are mainly 
used for food, and the various arrowroots contain starches 
recommended as particularly desirable for invalids. 
The principal commercial importance of refined starch, 
however, comes from the fact that when in contact with 
hot water its grains swell up and burst, forming a thick 
adhesive paste. This may be best brought about by 
mixing starch with cold water and slowly pouring the 
thick milky fluid into boiling water which is meanwhile 
agitated by constant stirring. The paste thus formed 
imparts to textile materials a high degree of lustre and 
that stiffness from which the name of starch (German, 
