THE SCIENCE OF BREATH - BY Yogi Ramacharaka 
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The Science of Breath, like many other teachings, has its esoteric or inner phase, as well as its exoteric or external. The physiological phase may be termed the outer or exoteric side of the subject, and the phase which we will now consider may be termed its esoteric or inner side. Occultists, in all ages and lands, have always taught, usually secretly to a few followers, that there was to be found in the air a substance or principle from which all activity, vitality and life was derived. They differed in their terms and names for this force, as well as in the details of the theory, but the main principle is to be found in all occult teachings and philosophies, and has for centuries formed a portion of the teachings of the Oriental Yogis.

In order to avoid misconceptions arising from the various theories regarding this great principle, which theories are usually attached to some name given the principle, we, in this work, will speak of the principle as Prana this word being the Sanscrit term meaning Absolute Energy Many occult authorities teach that the principle which the Hindus term Prana is the universal principle of energy or force, and that all energy or force is derived from that principle, or, rather, is a particular form of manifestation of that principle. These theories do not concern us in the consideration of the subject matter of this work, and we will therefore confine ourselves to an understanding of prana, as the principle of energy exhibited in all living things, which distinguishes them from a lifeless thing. We may consider it as the active principle of life-Vital Force, if you please. It is found in all forms of life, from the amoeba to man -from the most elementary form of plant life to the highest form of animal life.