'The living body, as the Helmholtz of the 1860’s conceived it, was a physical structure the behaviour of which could be characterized in terms of mathematical laws. As such, it constituted a medium through which impulses from the external world were conveyed to the mind. Whilst nerves were conveyors of sensory stimulations, it was the function of a physiologically-inaccessible mind to arrive at judgements regarding nature. Mind and sense organs thereby formed two elements of a perceptual system that retained a distinct separation between the immediate physiological conditions of sensation and their (physiologically-undetermined) apprehension (Lenoir 1993, 123-125; Turner 1994, 73-80). Helmholtz’s sensory model had not gone unopposed however. Starting in 1863, Hering had waged a lengthy campaign against any separate consideration of sensations and sense-organs themselves. Hering and his supporters drew on a longer-established tradition of psycho-physiological research to develop a sophisticated set of demonstrations and arguments identifying visual illusions not with the inaccurate judgements of a physiologically-independent mind, but with the physiological make-up of the organs of sense (Turner 1994, 89-93).'