There are four collections or Sa@mhitas, namely @Rg-Veda, Sama-Veda, Yajur-Veda and Atharva-Veda. Of these the @Rg-Veda is probably the earliest. The Sama-Veda has practically no independent value, for it consists of stanzas taken (excepting only 75) entirely from the @Rg-Veda, which were meant to be sung to certain fixed melodies, and may thus be called the book of chants. The Yajur-Veda however contains in addition to the verses taken from the @Rg-Veda many original prose formulas. The arrangement of the verses of the Sama-Veda is solely with reference to their place and use in the Soma sacrifice; the contents of the Yajur-Veda are arranged in the order in which the verses were actually employed in the various religious sacrifices. It is therefore called the Veda of Yajus--sacrificial prayers. These may be contrasted with the arrangement in the @Rg-Veda in this, that there the verses are generally arranged in accordance with the gods who are adored in them. Thus, for example, first we get all the poems addressed to Agni or the Fire-god, then all those to the god Indra and so on. The fourth collection, the Atharva-Veda, probably attained its present form considerably later than the @Rg-Veda. In spirit, however, as Professor Macdonell says, "It is not only entirely different from the _Rigveda_ but represents a much more primitive stage of thought. While the _Rigveda_ deals almost exclusively with the higher gods as conceived by acomparatively advanced and refined sacerdotal class, the _Atharva-Veda_ is, in the main a book of spells and incantations appealing to the demon world, and teems with notions about witchcraft current among the lower grades of the population, and derived from an immemorial antiquity. These two, thus complementary to each other in contents are obviously the most important of the four Vedas [Footnote ref 5]."