"Left to herself, the serpent now began, To change; her elfin blood in madness ran." - These lines are written by -

John Keats:- Born: October 31, 1795, London, England—- Death: February 23, 1821, Rome, papal list.- English Romantic lyric poet who devoted his short life to the perfection of a poetry. - - His writings were marked by vivid imagery, great sensuous appeal, and an attempt to express a philosophy through classical legend.- John Keats was apprenticed to a surgeon in 1811. Best Works:- Ode to Psyche- Ode on Melancholy- To Autumn- Bright Star- On First Looking into Chapman's Homer- Lamia- The Eve of St- La Belle Dame sans MerciSource: Britannica.comThese lines mentioned in the question are from the poem "Lamia".Lamia [Left to herself]John Keats"Left to herself, the serpent now began To change; her elfin blood in madness ran, Her mouth foam'd, and the grass, therewith besprent, Wither'd at dew so sweet and virulent; Her eyes in torture fix'd, and anguish drear,Hot, glaz'd, and wide, with lid-lashes all sear, Flash'd phosphor and sharp sparks, without one cooling tear."