Those who wish to invigorate themselves quickly should practise for two or three minutes what has been variously called deep breathing, diaphragmatic breathing, and abdominal breathing. Expel the breath vigorously, then with palms resting on the lower ribs take in very slowly a deep breath, stretching out the diaphragm muscle while doing so, then exhale somewhat less slowly. Repeat this exercise until feeling freshly renewed. A variant of this is practised in hatha yoga, but it is not recommended to those working without a competent hatha yoga teacher, because it has its own dangers. This variant consists in holding the breath before exhaling it and the exhalation itself is done with a hissing noise. All breath holdings can be dangerous. If the breath is held for too long, consciousness is lost, and what is too long for one person may not be for another.
-- Notebooks Category 5: The Body > Chapter 6 : Breathing Exercises > # 18
