The practice of Yoga has its roots in the fact that fasting and other physical mortifications induce a mental state in which the subject thinks that he has supernatural experiences[661].  Among many savage tribes, especially in America, such fasts are practised by those who desire communication with spirits.  In the Yoga philosophy these ideas appear in a refined form and offer many parallels to European mysticism.  The ultimate object is to dissociate the soul from its material envelopes but in the means prescribed we can trace two orders of ideas.  One is to mortify the body and suppress not only appetite and passion but also discursive thought:  the other is to keep the body in perfect health and ease, so that the intelligence and ultimately the soul may be untroubled by physical influences.  These two ideas are less incongruous than they seem.  Many examples show that extreme forms of asceticism are not unhealthy but rather conducive to long life and the Yoga in endeavouring to secure physical well-being does not aim at pleasure but at such a purification of the physical part of man that it shall be the obedient and unnoticed servant of the other parts.  The branch of the system which deals with method and discipline is called Kriya-yoga and in later works we also find the expression Hatha-yoga, which is specially used to designate mechanical means (such as postures, purification, etc.) prescribed for the attainment of various mental states.  In contrast to it is Raja-yoga, which signifies ecstasy and the method of obtaining it by mental processes.  The immediate object of the Kriya-yoga is to destroy the five evils[662], namely ignorance, egoism, desire, aversion and love of life:  it consists of asceticism, recitations and resignation to God, explained as meaning that the devotee fasts, repeats mantras and surrenders to God the fruit of all his works and, feeling no more concern for them, is at peace.  Though the Yoga Sutras are theistic, theism is accessory rather than essential to their teaching.  They are not a theological treatise but the manual of an ancient discipline which recognizes devotional feelings as one means to its end.  The method would remain almost intact if the part relating to the deity were omitted, as in the Sankhya.  God is not for the Yoga Sutras, as he is for many Indian and European mystics, the one reality, the whence and whither of the soul and world.

Eight branches of practice[663] are enumerated, namely:—­

1.  Yama or restraint, that is abstinence from killing, lying, stealing, incontinence, and from receiving gifts.  It is almost equivalent to the five great precepts of Buddhism.

2.  Niyama or observance, defined as purification, contentment, mortification, recitation and devotion to the Lord.

Purification is treated at great length in the later treatises on Hatha-yoga under the name of Shat-karma or sixfold work.  It comprises not only ordinary ablutions but cleansing of the internal organs by such methods as taking in water by the nostrils and discharging it by the mouth.  The object of these practices which, though they assume queer forms, rest on sound therapeutic principles, is to remove adventitious matter from the system and to reduce the gross elements of the body[664].