In the 1800s, humoral understandings of leprosy successively give way to disease models based on morbid anatomy, physiopathology, and bacteriology. Linkages between these disease models were reinforced by the ubiquitous seed/soil metaphor deployed both before and after the identification of M.leprae. While this metaphor provided a continuous link between medical descriptions, Henry Vandyke Carter's On leprosy (1874) marks a convergence of different models of disease. Simultaneously, this metaphor can be traced in popular medical debates in the late nineteenth century, accompanying fears of a resurgence of leprosy in Europe. Later the mapping of the genome ushers in a new model of disease but, ironically, while leprosy research draws its logic from a view of the world in which a seed and soil metaphor expresses many different aspects of the activity of the disease, the bacillus itself continues to be unreceptive to cultivation.