(FROM HIS SCIENCE PRIMER, INTRODUCTION.)

BY PROFESSOR, T. H. HUXLEY.


[Illustration]

Every one has seen a cornfield. If you pluck up one of the innumerable
wheat plants which are fixed in the soil of the field, about harvest
time, you will find that it consists of a stem which ends in a root at
one end and an ear at the other, and that blades or leaves are
attached to the sides of the stem. The ear contains a multitude of
oval grains which are the seeds of the wheat plant. You know that when
these seeds are cleared from the husk or bran in which they are
enveloped, they are ground into fine powder in mills, and that this
powder is the flour of which bread is made. If a handful of flour
mixed with a little cold water is tied up in a coarse cloth bag, and
the bag is then put into a large vessel of water and well kneaded with
the hands, it will become pasty, while the water will become white. If
this water is poured away into another vessel, and the kneading
process continued with some fresh water, the same thing will happen.
But if the operation is repeated the paste will become more and more
sticky, while the water will be rendered less and less white, and at
last will remain colorless. The sticky substance which is thus
obtained by itself is called gluten; in commerce it is the substance
known as maccaroni.

If the water in which the flour has thus been washed is allowed to
stand for a few hours, a white sediment will be found at the bottom of