the mesenteric glands; and, as each one receives its portion of chyle, a
wonderful thing happens. About half of it is changed into small round
bodies called corpuscles, and they float with the rest of the milky fluid
through delicate pipes which take it to a sort of bag just in front of the
spine. To this bag is fastened another pipe or tube--the thoracic
duct--which follows the line of the spine; and up this tube the small
bodies travel till they come to the neck and a spot where two veins meet.
A door in one opens, and the transformation is complete. The small bodies
are raw food no more, but blood, traveling fast to where it may be
purified, and begin its endless round in the best condition. For, as you
know, venous blood is still impure and dirty blood. Before it can be
really alive it must pass through the veins to the right side of the
heart, flow through into the upper chamber, then through another door or
valve into the lower, where it is pumped out into the lungs. If these
lungs are, as they should be, full of pure air, each corpuscle is so
charged with oxygen, that the last speck of impurity is burned up, and it
goes dancing and bounding on its way. That is what health means: perfect
food made into perfect blood, and giving that sense of strength and
exhilaration that we none of us know half as much about as we should. We
get it sometimes on mountain-tops in clear autumn days when the air is
like wine; but God meant it to be our daily portion, and this very
despised knowledge of cookery is to bring it about. If a lung is
imperfect, supplied only with foul air as among the very poor, or diseased
as in consumption, food does not nourish, and you now know why. We have
found that the purest air and the purest water contain the largest
proportion of oxygen; and it is this that vitalizes both food and, through
food, the blood.

To nourish this body, then, demands many elements; and to study these has
been the joint work of chemists and physiologists, till at last every