the blood was central to fludd's conception of the relationship between the microcosm and macrocosm; the blood and the spirit it circulated interacted directly with the spirit conveyed to the macrocosm. the macrocosmal spirit, carried by the sun, was influenced by astral bodies and changed in composition through such influence. comparatively, the astral influences on the macrocosmal spirit could be transported to the microcosmal spirit in the blood by the active commerce assumed between the macrocosm and the microcosm. fludd extended this interaction to his conception of disease: the movement of spirit between the macrocosm and microcosm could be corrupted and invade the microcosm as disease. like paracelsus, fludd conceived of disease as an external invader, rather than a complexional imbalance.