Sir Morell Mackenzie's 1889 treatise examines speech as the physiological power to modify vocal sound into distinct elements, distinguishing it from language as the particular manifestation of this universal faculty. He traces the voice's origin to sexual attraction and emotional expression, arguing that vocal organs developed through practice and association with emotional states. Mackenzie establishes that vocal sound is produced solely in the larynx, a complex musical instrument, and clarifies misconceptions about voice production.