Preparatory drawings for this composition are in the Landesmuseum, Oldenburg (W. Tischbein (ed. P. Reindl), Die Eselsgeschichte, Oldenburg, 1987, figs. 41 and 63).
The second drawing at Oldenburg is inscribed with the humours' identifications: from left to right Sanguine, Phlegmatic, Choleric and Melancholic. The heads above and below are middle positions between these extremes, a problem of combination touched on by Tischbein in his manuscript note to the preparatory drawing.
(2) Illustrated in plate IV, p. 135.