Glass delusion is an external manifestation of a psychiatric disorder recorded in Europe mainly in the late Middle Ages and early modern period (15th to 17th centuries).
[2] Robert Burton's The Anatomy of Melancholy (1621) touches on the subject in the commentary as one of many related manifestations[4] of the same anxiety: Fear of devils, death, that they shall be so sick, of some such or such disease, ready to tremble at every object, they shall die themselves forthwith, or that some of their dear friends or near allies are certainly dead; imminent danger, loss, disgrace still torment others; that they are all glass, and therefore will suffer no man to come near them; that they are all cork, as light as feathers; others as heavy as lead; some are afraid their heads will fall off their shoulders, that they have frogs in their bellies, Etc.
[5]Miguel de Cervantes based one of his short Exemplary Novels, The Glass Graduate (Spanish: El licenciado Vidriera, 1613), on the delusion of the title subject, an aspiring young lawyer.
[7] French philosopher René Descartes wrote Meditations on First Philosophy (1641), using the glass delusion as an example of an insane person whose perceived knowledge of the world differs from the majority.
[8] In An Essay Concerning Human Understanding (Book II, Chapter XI, 13) when proposing his celebrated model of madness, John Locke also refers to the glass delusion.
He failed to adequately respond to the Great Offensive that turned the war in the Turks' favour because he believed that his legs were made of glass and could shatter if he moved.