In ancient times when those who pursued yoga practices usually retired to peaceful forests and rugged mountains, lived simple disciplined lives, ate less rather than more, took little or no flesh food, and kept settlements, they were often out of reach both of professional medical help and professionally prescribed medicines--so they usually learnt to depend on wild-growing herbs as far as these were available, and on applications of intense pressure applied to diseased parts of the body or to the breathing process. The healing herbs are Nature's gift to man and many of them have indeed been incorporated in the pharmacopoeia used by modern Western scientific medicine but more wait to be added. The pressures have possibilities of being equally efficacious but, like a double-edged sword, constitute at one and the same time an instrument of some power and some danger. We have seen both striking cures and terrible disasters follow the practice of these physical yoga exercises when done without the careful personal supervision of a trained teacher and in several cases even when this supervision was available. Our final conclusion is that it is not enough to have a teacher who merely knows how to do them. It is really necessary to have during the earlier attempts the watchful supervision or veto of a qualified medical man who understands the anatomical dangers and physiological changes involved.
-- Notebooks Category 5: The Body > Chapter 5: Exercise > # 76