A form of Sweat afterwards endemic in Normandy.
The Picardy sweat, which was first noticed as a disease of the soil about the year 1717, and has continued off and on down to recent years, was indigenous to the departments in the basin of the Seine, from the Pas de Calais to Calvados, with Rouen as a centre. Why that strange form of sickness should have sprung up there and continued, now in one town or village now in another, with few blank years for a century and a half, no one can venture to say. It was not the English sweat in all its circumstances; on the contrary it was only rarely epidemic over a large population or a large tract of country at once. It was ordinarily limited to one or two spots at a time, and in the individuals affected it ran a longer course than the English sweat had done. But whenever it did become widely prevalent it also became a short and sharp infection like the English sweat, causing in some years a very considerable number of deaths. Distinctively the Picardy sweat was a somewhat mild sickness of a week or more, seldom fatal, distinctively also of a single town or village, or small group of villages. It was not unknown in some other parts of France, such as the Vosges and Languedoc, in Bavaria and in Northern Italy; but in these other localities it has been much more occasional or even rare. Its distinctive habitat for a century and a half has been the lower basin of the Seine; and there it has been so steady at one point or another from year to year throughout the whole of that period that it may be said to be a disease of the soil, indigenous or domesticated, and depending for its periodic manifestations mostly upon vicissitudes of the seasons, as affecting probably the rise and fall of the ground-water. It has been more a disease of the well-to-do bourgeois class than of the very poor, and it has often shown a preference for the cleaner villages. It has been the subject of a very large number of French writings from the year 1717 down almost to the present date. Strange as this form of disease is, neither its circumstances nor its nosological characters are left in any doubt; it is at once mysterious and perfectly familiar[533].