MH page 272

In order to have good blood, we must breathe well. Full, deep inspirations of pure air, which fill the lungs with oxygen, purify the blood. They impart to it a bright color and send it, a life-giving current, to every part of the body. A good respiration soothes the nerves; it stimulates the appetite and renders digestion more perfect; and it induces sound, refreshing sleep.

Deep breathing of pure air purifies the blood and promotes nerve, digestive, and sleep health. The passage makes several direct physiological claims regarding respiration and bodily functions.

The lungs should be allowed the greatest freedom possible. Their capacity is developed by free action; it diminishes if they are cramped and compressed. Hence the ill effects of the practice so common, especially in sedentary pursuits, of stooping at one's work. In this position it is impossible to breathe deeply. Superficial breathing soon becomes a habit, and the lungs lose their power to expand. A similar effect is produced by tight lacing. Sufficient room is not given to the lower part of the chest; the abdominal muscles, which were designed to aid in breathing, do not have full play, and the lungs are restricted in their action.

Lung capacity is maintained by free movement and diminished by stooping postures and tight lacing. This paragraph asserts anatomical changes in lung capacity based on posture and clothing habits.