In 1831, British physiologist Marshall Hall proposed five principles that he believed should govern animal experimentation. First, an experiment should never be performed if the necessary information could be obtained by observations; second, no experiment should be performed without a clearly defined and obtainable, objective; third, scientists should be well-informed about the work of their predecessors and peers in order to avoid unnecessary repetition of an experiment; fourth, justifiable experiments should be carried out with the least possible infliction of suffering (often through the use of lower, less sentient animals); and finally, every experiment should be performed under circumstances that would provide the clearest possible results, thereby diminishing the need for repetition of experiments.