On the cover is used the lithograph Two young men are approached by a prostitute: she is a clothed skeleton holding a made-up mask in front of her face, representing syphilis, by J. J. Grandville, [1830], 22,2 x 30,4 cm. The original image is archived in Wikimedia Commons (CC BY-NC 4.0). See  https://wellcomecollection.org/works/uxhrkm7n/items.