The first title, in 1 volume, was published in 1776; the second work in 2 vols., supplementing the first work, was published in 1778. In these two bioclimatological and biogeographical studies of disease in Normandy, on which he worked for fifteen years, Le Pecq provided case histories as well as detailed analyzes of epidemics and their relationship to climate, geography, water sources, and local customs, writing in his first work that doctors must study sickness in its natural habitat before they could treat large-scale health issues.