over the land the bacteria will be destroyed, for like most
bacteria, such as those which lurk in milk pails to sour the milk,
they are killed by the sunshine."

" That's right," said the grandmother. "That's the way to sterilize
milk pails and pans and crocks. I like crocks better than pans. They
don't have any sort of joints to dig out."

"Of course," continued Percy, "a wagon load of infected soil will
make a more perfect inoculation than a hundred pounds, and where it
costs nothing but the hauling it is well to use a liberal amount."

"How deep should it be taken?" asked Mr. West.

"About the same depth as you would plow. The tubercles are mostly
within six or eight inches of the surface. The bacteria depend upon
the nitrogen of the air and this must enter the surface soil.
Sometimes in wet weather the tubercles can be found almost at the
surface of the ground, and when the ground cracks one can often find
tubercles sticking out in the cracks an inch or two beneath the
surface but protected from direct sunshine.

"These bacteria have power to furnish very large amounts of nitrogen
to such a crop as alfalfa. The Illinois Station reports having grown
eight and one-half tons of alfalfa per acre in one season. It was
harvested in four cuttings. The hay itself was worth at least $6 a
ton above all expenses, which would bring $51 an acre net profit for
one year. Of course this was above the average, which is only about
four and one-half tons over a series of several years. But suppose
you can save only three tons and get $6 a ton net for it, as you