In 1844 Martineau underwent a course of mesmerism, returning to health after a few months. There was national interest in mesmerism at this time. Also known as 'animal magnetism', it can be defined as a "loosely grouped set of practices in which one person influenced another through a variety of personal actions, or through the direct influence of one mind on another mind. Mesmerism was designed to make invisible forces augment the mental powers of the mesmeric object." She eventually published an account of her case in 16 "Letters on Mesmerism", which caused much discussion. Her work led to friction with "the natural prejudices of a surgeon and a surgeon's wife" (i.e., her brother-in-law, Thomas Michael Greenhow and her sister, Elizabeth Greenhow, née Martineau).