The History of coloured Hearing. Origins of the synesthesies

Up to a quarter of a century ago, the time of the first version of this essay, it was almost completely unknown, having dropped into oblivion after a period of great interest that started in the Belle Époque. This paper follows the stages that led to the casual discovery (in a certain way similar to a case of serendipity) of subjective synesthesias and in particular investigates the French-Italian medical contribution, even though starting from a German academic document that is considered to be at the head of chain of references which, however, reveal themselves as a chain of equivocations (by doctors, before the historians). This investigation covers the crucial 70 years from the degree thesis