‘Even a potato in a dark cellar has a certain low cunning about him which serves him in excellent stead. He knows perfectly well what he wants and he knows how to get it […] If it be urged that the action of the potato is chemical and mechanical only […] the answer would seem to lie in an inquiry whether every sensation is not chemical and mechanical, whether those things which we deem the most spiritual are anything other but disturbances of equilibrium in a finite series of levers, beginning with those that are too small for microscopic detection, and going up to the human arm and the appliances which it makes use of?’