for lack of knowledge." And it is this lack of knowledge which it is
woman's special business to supply, in first training her household
to intelligence as the indispensable road to virtue and happiness.

The above statements will be illustrated by some account of the manner
in which the body is supplied with healthful nutriment. There are two
modes of nourishing the body, one is by food and the other by air. In
the stomach the food is dissolved, and the nutritious portion is
absorbed by the blood, and then is earned by blood-vessels to the
lungs, where it receives oxygen from the air we breathe. This oxygen
is as necessary to the nourishment of the body as the food for the
stomach. In a full-grown man weighing one hundred and fifty-four pounds,
one hundred and eleven pounds consists of oxygen, obtained chiefly
from the air we breathe. Thus the lungs feed the body with oxygen, as
really as the stomach supplies the other food required.

The lungs occupy the upper portion of the body from the collar-bone
to the lower ribs, and between their two lobes is placed the heart.

[Illustration: Fig. 22.]
[Illustration: Fig. 23.]
[Illustration: Fig. 24.]
[Illustration: Fig. 25.]
[Illustration: Fig. 26.]

Fig. 22 shows the position of the lungs, though not the exact shape.
On the right hand is the exterior of one of the lobes, and on the left
hand are seen the branching tubes of the interior, through which the
air we breathe passes to the exceedingly minute air-cells of which the
lungs chiefly consist. Fig. 23 shows the outside of a cluster of these