In the 1870s, Claude Bernard promoted a new physiological program for reforming medical research. Founded on a holistic view of the body and experimentalism--vivisection in particular--physicians would not consider organs, tissues, or other histological units in isolation, as rather as part of the body system. Bernard separated the interior environment of the body from the external environment of nature, thus opening to investigation the “black box” of the earlier thermodynamicists. This perspective influenced many including Louis Pasteur, who applied it novelly to single-celled organisms.