There remains another line of research, which is relatively unimportant, yet should be noted when the question of Greek influence is raised. It has been stated that Greek words are used in Latin sequences, thereby proving contact with Greek-speaking contemporaries on the part of their authors, or with Greek literary sources. Whenever this test is applied to any medieval writing produced by churchmen it should not be forgotten that the Vulgate was the one great continuous source, inspiration and standard of the Latin language as employed in the Middle Ages. Throughout the period, all Latin hymns which include a narrative element or refer in any other way to biblical statements are greatly indebted to the Vulgate. A considerable number of Greek words, naturally, appear in the Vulgate. Applying the criterion of Greek words to Notker’s sequences, one reaches no definitive results whatever. In the forty-one sequences attributed to Notker by Wilmanns, some seven Greek words appear which are not in the Vulgate.[27] If this proves anything in Notker’s case, it is significant only in connection with other evidence from Greek originals which has not been advanced. Having considered the separate development of the musical and poetical aspects of the sequence, as far as they can be sundered, it remains to view certain factors which may have affected that development but have not as yet been stated. The history of medieval music, quite apart from the creation of the _iubilus_ and the _sequentia_, should not be overlooked by the student who is trying to understand liturgical music in this general period. Perhaps during the eighth and certainly from the ninth century, polyphonic and harmonic forms began to appear. New melodies for sequences were in demand and were produced, which in turn were influenced by popular and secular music, with an interaction of words and music taking place, sometimes with words, sometimes with music leading the way.[28] The history of the sequence, when complete, will owe much to the studies of medieval music now in progress by musicologists, some of whose conclusions have been noted above. The history of musical instruments is relevant here but in any case it must always be remembered that the church possessed the musical notation and was able to dominate the field.