French scientist Léon Dumont had drawn, in an earlier essay about the biological consequences of habit, between the actions of water on land and the effects of experience on the brain: “Flowing water hollows out a channel for itself which grows broader and deeper; and when it later flows again, it follows the path traced by itself before. Just so, the impressions of outer objects fashion for themselves more and more appropriate paths in the nervous system, and these vital paths recur under similar external stimulation, even if they have been interrupted for some time.”6
