I’ve just found a fascinating article in the History of Psychiatry about a type of delusion that was widely reported in the 15th to 17th centuries but rarely occurs in modern times. The reports were of patients who believed that they were made of glass and thought they might shatter if they suffered even the lightest of knocks.
In some of the more unusual forms, people struck with this form of madness might even consider themselves to be an oil lamp, a drinking vessel or even trapped in glass bottle.
The belief could even be specific to certain parts of the body:
Reports of glass bones, arms, and legs appeared much later, but Early Modern accounts were particularly rich in allusions to glass hearts/chests, and fragile heads. Tommaso Garzoni, an Italian monk,wrote a series of character sketches of mentally-disturbed people in 1586. In one of these cameos, drawn from Galen, the fragile delusion presents as a man who thought that his body consisted of only a large head, which he protected from injury by avoiding all contact with his fellows.
The delusion was reported in medical and the proto-scientific literature of the time, but also shows up in plays and literature.
Reportedly, one famous sufferer was King Charles VI of France, who allegedly refused to allow people to touch him, and wore reinforced clothing to protect himself.
While we tend to be most interested in how new delusional themes arise in response to cultural developments, we pay much less attention about delusions which were once common but now rarely occur.
This is a lovely example of a very well researched look at the history of no-longer popular delusions.
It’s also worth noting that Wikipedia has a page on the delusion where someone has briefly summarised some of the main points of the article.