In Boerhaave and his commentator Van Swieten, mania naturally forms the superior degree of melancholy, not simply on account of the frequent metamorphosis, but through the effect of a necessary dynamic concatenation: the cerebral fluid, which stagnates in bilious patients, after a certain time becomes agitated, as the immobility of the black bile that engorges the viscera makes it 'more acrid and noxious'.