of
iron in his blood.
The reason why iron is able to serve this unique purpose of conveying
life-giving air to all parts of the body is because it rusts so readily.
Oxidation and de-oxidation proceed so quietly that the tenderest cells
are fed without injury. The blood changes from red to blue and _vice
versa_ with greater ease and rapidity than in the corresponding
alternations of social status in a democracy. It is because iron is so
rustable that it is so useful. The factories with big scrap-heaps of
rusting machinery are making the most money. The pyramids are the most
enduring structures raised by the hand of man, but they have not
sheltered so many people in their forty centuries as our skyscrapers
that are already rusting.
We have to carry on this eternal conflict against rust because oxygen is
the most ubiquitous of the elements and iron can only escape its ardent
embraces by hiding away in the center of the earth. The united elements,
known to the chemist as iron oxide and to the outside world as rust, are
among the commonest of compounds and their colors, yellow and red like
the Spanish flag, are displayed on every mountainside.
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