Before Lister's studies of surgery, many people believed that chemical damage from exposure to "bad air", or "miasma", was responsible for infections in wounds. Hospital wards were occasionally aired out at midday as a precaution against the spread of infection via miasma, but facilities for washing hands or a patient's wounds were not available. A surgeon was not required to wash his hands before seeing a patient; in the absence of any theory of bacterial infection, such practices were not considered necessary. Despite the work of Ignaz Semmelweis and Oliver Wendell Holmes Sr., hospitals practised surgery under unsanitary conditions. Surgeons of the time referred to the "good old surgical stink" and took pride in the stains on their unwashed operating gowns as a display of their experience.