50.  Yatra is not to be taken as a locative here.  It is equivalent to yatah or for which.

51.  Tasmin is taken, by Nilakantha as Apana sahite Prane.

52.  Utkarshena anayati, hence Udana, says Nilakantha.  The sense of the whole passage seems to be this.  Worldly life is regulated by the life-breaths.  These are attached to the Soul and lead to its individual manifestations.  Udana controls all the breaths.  Udana is controlled by penance.  It is penance then that destroys the round of rebirths and leads to absorption into Brahman.

53.  The meaning seems to be this:  they who renounce sensuous objects can create them when they like.  One casting off smell that has earth for its object can create earth when he likes.

54.  What is stated in this passage is, shortly, this:  the ear, etc, are the Hotris or sacrificing priests who are to pour libations on the sacrificial fire.  The perceptions and functions of those organs constitute the Havi or libations that are to be poured.  The points, wind, etc, are the Agni or sacred fires on which they are to be poured.  These statements are recapitulated in verse 5.  The objects of the senses, of the same as those in verse 3, are the fuel, previously described as Havi or libations, which are to be burnt off by being cast into the fires.

55.  The Hridaya or heart is the Garhapatya fire.  From it is produced another fire, the Ahavaniya, viz., the mind.  ’The heart was pierced.  From the heart arose mind, for the mind arose Chandramas,’ is the declaration of the Sruti cited by Nilakantha.  The Ahavaniya fire or mind is the mouth.  Asyam ahavaniya is the Sruti.  Annamayam hi Somya manas, apomayah pranah, tejomayi vak is the Sruti that bears upon this.  Food or fire, poured into the mouth develops into speech or word.  Vachaspati implies the Veda or word.  First arises the word, the mind sets itself upon it, desirous of creation.  This corresponds with the Mosaic Genesis.—­’God said; let there be light, and there was light.’  The word was first.

56.  The last question seems to be this:  in dreamless slumber, the mind disappears totally.  If it is the mind upon which Prana rests, why does not Prana also disappear?  It is seen to separate itself from mind, for it continues to exist while mind does not exist.  If so, i.e., if existing, as it must be admitted to do, why does it not apprehend objects?  What is it that restrains its powers of apprehension?

57.  Bhutatmanam is ordinary Prajapati.  Nilakantha takes it to mean here individual Jiva or self.

58.  It is, through words that desirable fruits, visible and invisible, are acquired.  Of course, word means both ordinary speech and Vedic Mantras.