More wisdom from the book YOGA and HEALTH by Selvarajan Yesudian and Elisabeth Haich, First published in 1953. (see my blog post 21 March – https://hathayogaipswich.com.au/2014/03/21/hatha-yoga-sun-and-moon/)
Every force is based on prana; the force of gravity, attraction, repulsion, electricity, radio-activity — without prana there is no life, for prana is the soul of all force and all energy. This prime principle is to be found everywhere in the world. It is in the air, but is not air; it is in food, but it is not food; it is the strength in the vitamin; it is also contained in water, but is not identical with the chemical constituents of water; these are merely carriers of prana.
The air is filled with free prana, and the human organism can most easily absorb prana from fresh air through the process of breathing, in breathing normally we take in normal amounts of prana. Through deep breathing our intake is increased, and through controlled Yoga breathing we are able to store up a substantial quantity of reserve prana in our brain and nerve centres to be used in case of necessity.
The most obvious manifestation of prana in the human body is the fact that it forces us to breathe. The result of this is the movement of our lungs. If we wish to get better acquainted with prana and learn consciously to store up more prana in our nerve centres, our first task is to control the movements of our lungs, that is, our breathing. This means that we cease to breathe haphazardly, irregularly, and unconsciously, and that we learn to take each breath consciously, with concentration of thought, leading the absorbed prana into the nerve centres that serve as storage areas. The conscious practice of controlling prana through concentration and regulated breathing is called pranayama. Pranayama is the most important basis of the system of Hatha Yoga. Prana is the fuel of the lung and the entire human body. If, through injury or a dis-ease resulting from unnatural living, the body becomes incapable of absorbing prana, the powerful life current is turned off just as the current of a transmitter ceases to flow through a damaged wireless set. It is still present in the universe, but it can no longer manifest itself. From the foregoing we are quite justified in stating, that without prana — whether we wish to call it ether, cosmic radiation or some other name — there could be no life on earth.
We can most easily curb dis-ease and likewise increase and maintain our life force if we give our organism more and fresher prana. Hatha Yoga and the pranayama it teaches must not be considered in the occident as a theory laden with oriental hocus-pocus. Pranayama is quite deserving of serious attention by western physicians.