Chandogya Upanishad is one of the oldest Upanishads written on the Vedic Brahmana period about ninth to eighth century B.C. Chandogya Upanishad is associated with Sama Veda. It is the part of Chandogya Brahaman that contains ten chapters. The 2nd Khanda of First Chapter of Chandogya Upanishad deals with meditation on Om as the Prana. The gods and the demons, both offspring of Prajapati once fought between themselves. The gods then collected the Udgitha thinking that it would help them defeat the Asuras (demons). Thus, the gods began meditating on the Udgitha i.e. the Om Mantra as the Prana that functions through the nose. The demons then contaminated with sin or evil. Thus, when one smell they experience both pleasant and foul smell. The gods then meditated on the Udgitha as speech. But the demons contaminated it with evil. Therefore, one speaks both truth and untruth as speech has been pierced by evil. The gods next meditated on the Udgitha as the eye. The demons again pierced it with evil. Therefore, one sees both worthy and unworthy things as the eye has been pierced by evil.
Next they adored ear as the Udgitha but the demons contaminated it with evil. Therefore, one hears both what is worth hearing and what is not worth hearing as the ear is pierced by evil. The gods then adored the mind as the Udgitha. But the demons pierced it with evil. Therefore, one thinks of both proper and improper thoughts as the mind is pierced by evil. Finally the gods together meditated on the Udgitha as the principal Prana or the vital breath. This time when the demons tried to hit it and contaminate it with evil they were scattered and destroyed. As a cluster of earth gets scattered on being hit by a stone, a person also becomes injured on trying to injure or contaminate the Prana with evil.
The principal Prana or the vital breath does not distinguish between what is pleasant smelling and what is foul smelling; for it is smitten by evil. Whatever a person eats or drinks with the vital breath supports the other Pranas. At the last moment, deprived of support, they depart, and make men gape at the time of their death.
Angira meditated on the Udgitha as the principal Prana hence it is called Angiras, because it is the essence of the limbs i.e. anga. Brihaspati meditated on the Udgitha as the principal Prana hence it is known as Brihaspati, because speech is great meaning brihat and it is the lord or pati of speech. Ayasya next meditated on the Udgitha as the principal Prana hence it is known as Ayasya as it comes (ayate) from the mouth (asya). Vaka, the son of Dalbhya, knew about the Prana. He became the udgatri priest of the sacrificers residing in the Naimisha forest. By singing the Udgitha he fulfilled all their desires. Thus, one who is aware of the Prana and meditates upon the imperishable Udgitha (Om) obtains all his desires by reciting the Udgitha.
