The case of Guido is typical of the period in which he lived. Very evidently an unusually gifted teacher, as Hucbald was a hundred years before him, his influence was strong over the communities with which he came into contact, and spread abroad after his death, so that many innovations which were probably the results of slow growth were attributed to his inventiveness. The _Micrologus_ contains many rules for the construction of organum below a _cantus firmus_, which are not very much advanced beyond those of Hucbald and Odo. The old strict diaphony is still held by him in respect, though the free is much preferred. To those intervals which result from the 'free’ treatment of the organizing voice, however, he gives names, and he is conscious of their effect; so that, where Hucbald and Odo confined themselves to giving rules for the movement of the organizing voice in such a way as to avoid the harsh tritone even at the cost of other dissonances, Guido gives rules to direct singers in the use of these dissonances for themselves, which, as we have seen, in the earlier treatises were considered accidental. This marks a real advance. But there is in Guido’s works the same attempt merely to make rules, to harness music to logical theory, that we found in Hucbald’s and Odo’s; and it is again hard to believe that his method of organizing was in common practice, or that it represents the style of church singing of his day. From the accounts of the early Christians, from the elaborate ornamentation of the plain-song in mediæval manuscripts in which it is first found written down, and from later accounts of the 'descanters’ we are influenced to believe that music was sung in the church with a warmth of feeling, sometimes exalted, sometimes hysterical even to the point of stamping with the feet and gesticulating, from which the standardized bald ornamentation of Guido is far removed. Furthermore, the next important treatises after Guido’s, one by Johannes Cotto, and an anonymous one called _Ad Organum Faciendum_, deal with the subject of organum in a wholly new way and show an advance which can hardly be explained unless we admit that a freer kind of organum was much in use in Guido’s day than that which he describes and for which he makes his rules.