It returns, if pure air has met it in the lung, with all corruption destroyed, a dancing particle of life.

But to be life, and not slow death, thirty-three hogsheads of air must pass daily into the lungs, and twenty-eight pounds of blood journey from heart to lungs and back again three times in each hour.

It rests wholly with ourselves, whether this wonderful tide, ebbing and flowing with every breath, shall exchange its poisonous and clogging carbonic acid and watery vapor for life-giving oxygen, or retain it to weigh down and debilitate every nerve in the body.
With every thought and feeling some actual particles of brain and nerve are dissolved, and sent floating on this crimson current.

With every motion of a muscle, whether great or small, with every process that can take place in the body, this ceaseless change of particles is going on.
Wherever oxygen finds admission, its union with carbon to form carbonic acid, or with hydrogen to form water, produces heat.

The waste of the body is literally burned up by the oxygen; and it is this burning which means the warmth of a living body, its absence giving the stony cold of the dead.