ntance but once in a thousand
years.

The business of transportation occupies the time and attention of
thousands of workers, and its ramifications are endless. It is not
limited to a particular region like agriculture, or to towns and
cities like manufacturing; it is not stopped by tariff walls or ocean
boundaries. An acre of wheat is cut by the reaper, threshed, and
carted to the elevator by wagon or motor truck. The railroad-car is
hauled alongside, and with other bushels of its kind the grain is
transported to a giant flour-mill, where it is turned into a whitened,
pulverized product, packed in barrels, and shipped across the ocean to
a foreign port. Conveyed by rail or truck to the bakery, the flour
undergoes transformation into bread, and takes its final journey to
hotel, restaurant, and dwelling-house. Similarly, every kind of raw
material finds its destination far from the place of its production
and is consumed directly or as a manufactured product. This gigantic
business of transportation is the means of providing for the
sustenance and comfort of millions of human beings, and in spite of
the extensive use of machinery it requires at every step the
co-operative labor of human beings.

212. =Growth of Interdependence.=--It is the far-flung lines of
commerce that bind together the peoples of the world. Formerly there
were periods of history, as in the European Middle Ages, when a social
group produced nearly everything that it needed for consumption and
commerce was small; but now all countries exchange their own products
for others that they cannot so readily produce. The requirements of
commerce have broken down the barriers between races, and have
compelled mutual acquaintance and knowledge of languages, mutual
confidence in one another's good intentions, and mutual understanding
of one another's wants. The demands of commerce have precipitated
wars, but have also brought victories of peace. They have stimulated
the invention of improved means of communication, as the demands of
manufacturing stimulated invention of machinery. The slow progress of
horse-drawn vehicles over poor roads provoked the invention of
improved highways and then of railroads. The application of steam to
locomotives and ships revolutionized commerce, and by the steady
improvements of many years has given to the eager trader and traveller
the speedy, palatial steamship and the _train de luxe_.

Transportation depends, however, on the