Yet no sweeping alteration was made in the system of vocal cultivation. Flexibility of voice was acquired through practice in the singing of individual parts of contrapuntal works, those being chosen which presented technical difficulties in a convenient form. This advanced stage of vocal training was undertaken only after the rudimentary principles of singing had been mastered in the sight-singing classes. In spite of the greater technical demands made on the voice, the proper management of the vocal organs was not seen to involve a problem of any difficulty. Sight singing classes numbered sometimes as many as forty pupils. The instructor in this primary grade was expected to see that the students sang clearly and in tune, and that they avoided the faults of nasality and throatiness. To the matter of tone production the teacher could of course pay very little attention, as the rudiments of music were the main subject of study. Yet the few hints and corrections occasionally given by the sight-singing teacher were all the instruction that the students received in the management of the voice. On the completion of the course in sight singing the students were expected to produce their voices properly, as well as to sing difficult music at sight. No pupil could be admitted to the classes for advanced instruction in singing whose voice was not properly controlled. IV Up to the latter part of the sixteenth century there was nothing to give promise of a sudden development of solo singing. Popular music had as a matter of fact consisted from time immemorial largely of singing by a single voice. The musical instincts of the great mass of the people had found expression in the folk-song, while the semi-cultured classes had long cultivated the arts of the various orders of Troubadours and Minnesingers. But these popular forms of music were looked upon by the trained musicians with a certain contempt. Music had to be sung in parts by several voices in order to be worthy of recognition as serious art. Polyphonic music utterly ignores the capabilities of beauty and expressiveness inherent in the single voice. When several melodies are sung at once, each one of equal importance with all the others, it is impossible for one voice to receive more attention than another. Yet a time came when music was forced to break the bonds of polyphony and free itself from the restraints imposed upon it by multiple part-writing. Greater command of beauty and expressiveness was precisely the end sought by those composers, notably Palestrina, whose work marks the culmination of the polyphonic school. The spirit of the time was seeking for greater freedom in the expression of the musical instinct and singers and musicians alike were moved by this spirit. Solo singing was the inevitable result of a pressing demand.