During the 18th century, oriented thinking about the origin of human knowledge, and the progress of ocular surgery, led to a number of observations on born blind recently cured from cataracts by famous surgeons. Such observations were continuously done during the 19th century, and they were interpreted either from the empiristic viewpoint or from the all along viewpoint. In 1820, Dr. Sebastien Guillie, manager and chief consultant at the Royal Institution for Younger Blind, prospected different experiments with four of his pupils, in order to prove the contagiousness of purulent ophtalmia. Despite the various differences between Dr. Guillie's experiments and his predecessors', the author voices that the century old habit of using blind people as subjects of experiment was the factor that allowed Guillie to grant permission using his pupils as guinea pigs.