Although __Y__ was credited with its discovery, he wasn't the original discoverer.
The use of bread with a blue mould (possibly __X__) as a means of treating suppurating wounds was a staple of folk medicine in Europe since the Middle Ages. The first published reference appears in the publication of the Royal Society in 1875, by John Tyndall (of the famous Tyndall Effect). Ernest Duchesne documented it in an 1897 paper, which was not accepted by the Institut Pasteur because of his youth.
In March 2000, doctors at the San Juan de Dios Hospital in San José, Costa Rica published the manuscripts of the Costa Rican scientist and medical doctor Clodomiro (Clorito) Picado Twight (1887–1944). They reported Picado's observations on the inhibitory actions of __X___between 1915 and 1927. Picado reported his discovery to the Paris Academy of Sciences, yet did not patent it, even though his investigations started years before __Y___.
Plenty of theme and answers clues, also workoutable from the name.
This is also the second last question of the theme round. All answers to be displayed by Sunday Morning, and the theme unveiled as well.
