“Each time we wish to understand a system whatever it is, we need a structure. What applies to modern science already applied to the ancient yogic sages when they were concerning themselves with the human system.
The method of the ancients was to reflect, to meditate and to attempt to find clear replies to their questions. They tried to give a form to what they wanted to understand, corresponding to what they already understood. In this way of proceeding, they did not differ from the sages of the ancient medical science of Āyurveda who also tried to understand the human organism in a particular way, nor from the doctor philosophers of ancient China.
Later, modern science, and Western science, have sought in their turn a method of classifying the human organism and have worked out their own way of presenting this.
Amongst the innumerable ideas developed by the yogis around the human system, some have become the foundation of all the other considerations. So the opinion that all aspects of our lives are supported by a particular energy was widespread among the sages; they called this life force ‘Prāṇa’.
Whilst Prāṇa circulates in us, we live, and when it goes, we die. Prāṇa is responsible for different functions in the body. Prāṇa expresses itself in everything that concerns life. There is an important question to be answered. How does Prāṇa penetrate the different areas of the body?”