But the most important point of all is this, that these hymns, which exist both in the Pada and Samhitâ texts, are quoted by the Prâtisâkhya, not only for general purposes, but for special passages occurring in them, and nowhere else. Thus in Sûtra 154, hetáyah is quoted as one of the few words which do not require the elision of a following short a. In order to appreciate what is implied by this special quotation, it is necessary to have a clear insight into the mechanism of the Prâtisâkhya. Its chief object is to bring under general categories the changes which the separate words of the Pada text undergo when joined together in the Ârshî Samhitâ, and to do this with the utmost brevity possible. Now the Sandhi rules, as observed in the Samhitâ of the Rig-veda, are by no means so uniform and regular as they are in later Sanskrit, and hence it is sometimes extremely difficult to bring all the exceptional cases under more or less general rules. In our passage the author of the Prâtisâkhya endeavours to comprehend all the passages where an initial a in the Veda is not elided after a final e or o. In ordinary Sanskrit it would be always elided, in the Samhitâ it is sometimes elided, and sometimes not. Thus the Prâtisâkhya begins in Sûtra 138 by stating that if the short a stands at the beginning of a pâda or foot, it is always elided. Why it should be always elided in the very place where the metre most strongly requires that it should be pronounced, does not concern the author of the Prâtisâkhya. He is a statistician, not a grammarian, and he therefore simply adds in Sûtra 153 the only three exceptional passages where the a, under these very circumstances,

happens to be not elided. He then proceeds in Sûtra 139 to state that a is elided even in the middle of a pâda, provided it be light, followed by y or v, and these y or v, again followed by a light vowel. Hence the Samhitâ writes to ऽvădan, soऽyăm, but not sîkshantoऽvratam, for here the a of avratam is heavy; nor mitramahoऽvadyât, for here the a following the v is heavy.

Then follows again an extension of this rule, viz. in the case of words ending in âvo. After these, a short a, even if followed by other consonants besides y or v, may be elided, but the other conditions must be fulfilled, i. e. the short a must be light, and the vowel of the next syllable must again be light. Thus the Samhitâ writes indeed gâvoऽbhĭtah, but not gâvoऽgman, because here the a is heavy, being followed by two consonants.