When we breathe normally we do not exhale all the air from our lungs, and this remaining carbon-dioxide gas ultimately produces death.
Year in and year out we have been infiltrating our bodies with this carbon-dioxide gas. We leave about a hundred cubic inches of this deadly gas in our lungs; for when we inhale we use three times the muscular energy than when we exhale. Only when we can develop our breathing muscles to a high degree as the Yogi does can we keep our lungs pure. By careful exercise we learn to breathe outwardly. When this becomes a habit our body will be greatly refreshed and our mind-atmosphere cleared of its debris.