In the eighteenth and nineteenth centuries congenital syphilis was a major cause of infant mortality in France but mercury, the preferred treatment for the disease, could not be safely given to infants. In the 1780s the Vaugirard hospital in Paris began to treat affected infants by giving mercury to wet nurses, who transmitted it to infants through their milk. Despite the highly contagious nature of syphilis and the dangerous side-effects of mercury, the practice of using healthy wet nurses to treat syphilitic infants spread throughout France and continued into the nineteenth century.