And as the oxygenated blood is carried to all parts of the system, building up and replenishing, so is the prana carried to all parts of the nervous system, adding strength and vitality.

If we think of prana as being the active principle of what we call "vitality," we will be able to form a much clearer idea of what an important part it plays in our lives.

Just as is the oxygen in the blood used up by the wants of the system, so the supply of prana taken up by the nervous system is exhausted by our thinking, willing, acting, etc., and in consequence constant replenishing is necessary.

Every thought, every act, every effort of the will, every motion of a muscle, uses up a certain amount of what we call nerve force, which is really a form of prana.

To move a muscle the brain sends out an impulse over the nerves, and the muscle contracts, and so much prana is expended.