Laguerre separates folk medical knowledge from the cosmopolitan medicine of hospitals and journals largely by how each is stored and passed on. Written knowledge accumulates, crosses borders and survives unaltered; oral knowledge belongs to a family or a locality, changes a little with every telling, and vanishes once the need it answered has gone.

Much of the book sorts the Afro-Caribbean repertoire into kinds: cures credited to a named discoverer or to a spirit who learned healing at the world's beginning, remedies that work by symbolic likeness, such as red food and drink for weak blood, and the division between what anyone may learn and what is inherited within cult groups and disclosed in dreams.

He then follows these traditions through the plantation, where the enslaved community's medical knowledge is treated as a collective memory reassembled under duress, and onward through Asian indenture and black migration to northern American cities, each encounter yielding fresh syncretism.