In the chandas , the na of (the Pronoun) nas is changed into ṇa , when it comes after a root having a ra or ṣa or after the words uru and ṣu (su),
Thus अग्ने रक्षाणः (Rig VII. 15. 13). 'O Agni protect us'. शिक्षा णो अस्मिन् (Rig. VII. 32. 26) 'Teach us this'. उरु :- उरुणस्कृधि (Rig. VIII. 75. 11) षु — अभीषुणः सखीनाम् (Rig IV. 31. 3). ऊर्ध्व ऊषुणः ऊतये (Rig. I. 36. 13).
The word नस् is here the pronoun नस्, which is the substitute, in certain cases, of अस्मद् 8.1.21 and does not mean here the नस् substitute of नासिका ॥ In the next sutra, however, both नस् are taken. धातुस्थ means 'that which exists in a dhatu', namely र् and ष् when occurring in a root. The word उरु means the word-form उरु; and षु means सुञ्, and is exhibited with ष-change. It does not mean the affix सु of the Locative Plural. Therefore, not here इन्द्रो धता गृहेषु नः ॥ The word रक्षा is the 2rd Person singular, Imperative, the lengthening is by 6.3.135. The root शिक्ष् has the sense of दान in the Veda. कृधी is 2nd Person singular Imperative of कृ 6.4.102, the visarga of नः is changed to स् by 8.3.50. In अभीषु there is lengthening by 6.3.134: so also in ऊषुणः &c.,