Although the language of these sagas and poems is not that of the glosses, but what is called "Middle-Irish," still it does not in the least follow that the poems and sagas belong to the Middle-Irish period. "The old Middle-Irish manuscripts," says Zimmer, "contain for the most part only Old Irish texts re-written."[9] "Unfortunately," says Windisch, "every new copyist has given to the text more or less of the linguistic garb of his own day, so that as far as the language of Irish texts goes, it depends principally upon the age of the manuscript that contains them."[10] And again, in his preface to Adamnan's vision, he writes: "Since we know that Irish texts were rewritten by every fresh copyist more or less regularly in the speech of his own day, the real age or a prose text cannot possibly be determined by the linguistic forms of its language."[11] It is much easier to tell the age of poetry than prose, for the gradual modification of language, altering of words, shortening of inflexions, and so on, must interfere with the metre, so that when we find a poem in a twelfth-century manuscript written in Middle Irish and in a perfect metrical form, we may--no matter to what age it is _ascribed_--be pretty sure that it cannot be more than two or three centuries older than the manuscript that contains it. Yet even of the poems Dr. Atkinson writes: "The poem _may_ be of the eighth century, but the forms are in the main of the twelfth."[12] Where poems that really are of ancient date have had their language modified in transcription so as to render them intelligible, the metre is bound to suffer, and this lends us a criterion whereby to gauge the age of verse, which is lacking to us when we come to deal with prose.