Task: Question Answering
Input (English): Passage: De Long's party found no immediate sign at their landing-place of any human habitation, and had only a sketchy idea of where they were—Petermann's map provided few useful details. On September 19, having buried their non-essential possessions in a mound marked by a tent pole, they set out in search of settlements. Progress was hampered by the poor physical condition of the men, in particular Eriksen, who was badly affected by frostbite. On September 21 they halted at two empty huts, probably part of a hunting camp, where Alexey raised spirits by shooting a deer to replenish their dwindling food stocks. De Long allowed his exhausted party several days' rest before resuming the march.On September 28 the party found a large hut, with signs of recent occupation–edible food in the store, and moccasin tracks in the snow. When searches in the locality brought no sign of people, De Long decided to move on. By October 4, Eriksen could not continue; the party halted at another abandoned hut where, on October 6, Eriksen died. On October 9, with the condition of several men worsening, De Long decided to send two of the fittest in the group, Nindemann and Noros, to seek help. Ambler was offered the opportunity to go with them, but felt that his duty as a doctor required him to stay with the main body.For the next week De Long's party struggled on, sometimes making barely a mile a day. Although they jettisoned more of their possessions on the way, De Long insisted on carrying his maps and journals. His entry for October 10 recorded that there was "nothing for supper but a spoonful of glycerine". A few days later Alexey, the group's principal hunter, shot a ptarmigan which provided soup. But Alexey was weakening, and on October 17 he died.On October 20, trapped by the weather and without supplies, the party came to a final halt. Throughout the march De Long had written up his journal each day, but after October 20 his entries became intermittent, largely limited to terse statements of the dying and the dead. He noted the deaths of Kaak and Lee on October 21, Iverson on the 28th, Dressler on the 29th. His last entry, dated October 30, records the deaths of Boyd and Görtz and ends "Mr Collins dying". 
Question: What is the name of the person who felt that his duty as a doctor required him to stay with the main body?
Output (English): Ambler.