George Mallory described the use of such oxygen as unsportsmanlike, but he later concluded that it would be impossible for him to summit without it and consequently used it on his final attempt in 1924. When Tenzing and Hillary made the first successful summit in 1953, they also used open-circuit bottled oxygen sets, with the expedition's physiologist Griffith Pugh referring to the oxygen debate as a futile controversy, noting that oxygen greatly increases subjective appreciation of the surroundings, which after all is one of the chief reasons for climbing. For the next twenty-five years, bottled oxygen was considered standard for any successful summit.