Upon reaching the left auricle of the heart, it is forced into the left ventricle, from whence it is again forced out through the arteries on its mission of life to all parts of the system.

It is estimated that in a single day of twenty-four hours, 35,000 pints of blood traverse the capillaries of the lungs, the blood corpuscles passing in single file and being exposed to the oxygen of the air on both of their surfaces.

When one considers the minute details of the process alluded to, he is lost in wonder and admiration at Nature's infinite care and intelligence.
It will be seen that unless fresh air in sufficient quantities reaches the lungs, the foul stream of venous blood cannot be purified, and consequently not only is the body thus robbed of nourishment, but the waste products which should have been destroyed are returned to the circulation and poison the system, and death ensues.

Impure air acts in the same way, only in a lessened degree.

It will also be seen that if one does not breathe in a sufficient quantity of air, the work of the blood cannot go on properly, and the result is that the body is insufficiently nourished and disease ensues, or a state of imperfect health is experienced.