El Colegio de Belén played a very important role in ridding the world of the scourge of the yellow fever.

The leading researcher and eventual discoverer of the way in which that killer disease was propagated in the 19th century, Dr. Carlos J. Finlay, had been the head doctor of the Jesuit community in Havana, Cuba.  He asked for volunteers to prove his theory that the disease was transmitted by the Aedes Aegypti mosquito, rather than by direct contact.  Between the 1870s and the 1890s over one hundred volunteers supplied a large enough sample to run a scientifically acceptable experiment.  Of these, 57 were Jesuit Fathers and Brothers or employees of the Society of Jesus at Belén.

Dr. Carlos J. Finlay (1833-1915) was born in Camaguey, Cuba.  He graduated from Jefferson Medical College in Philadelphia in 1855, one year after the opening of  Colegio de Belén in Havana.  A hundred years later he was recognized by the International Congress of Medicine as the discoverer of the method of transmission of the disease.  This discovery saved thousands of lives in the tropics, most of all during the construction of the Panama Canal.

According to tradition, Dr. Finlay had come up with his theory while saying a rosary, during which time a mosquito landed on his hand.

In the front Lobby of the Colegio de Belén in Marianao there was a large memorial wall honoring Dr. Finlay, the volunteers and the three martyrs who lost their lives as a result of the experiment.