Why does Paul refuse to be chloroformed after his injury in All Quiet on the Western Front?

Paul refuses to be "put under" because he fears that the surgeon will amputate his injured leg.

In Chapter 10 of All Quiet on the Western Front, after having three weeks of good food and relaxation as Paul and the others guard a deserted village and a supply dump, the men are sent to the front. There they see the few people who remain out. Soon, the air screams with shells, and Paul forgets to "do the right thing under fire" and a "blow sweeps like a whip" over his left leg. He hears Albert beside him cry out, and he yells for Albert to get up quickly. They run and fall over a hedge. With their faces smothered with duck-weed, they stay in the ditch that is filled with water and keep their heads down when they hear shells whistling. When they can, they run until they reach a small dug-out. There they bandage each other. Albert's shot is just above his knee on his right leg; Paul is injured in both leg and arm, but Albert dresses his wounds. 

Because he can crawl some, Paul calls out to a passing ambulance. The driver gives them an anti-tetanus shot and takes them to a dressing station, where they fear that the surgeon will amputate their legs. Paul knows that 

...the surgeons in the dressing stations amputate on the slightest provocation...[because it] is much simpler than complicated patching"

He and Albert both fear being made cripples for the rest of their lives. When Paul refuses the chloroform, the doctor pokes around in his wounded leg, causing Paul such pain that he tries to "crash into the surgeon's spectacles" until the angered surgeon orders, "Chloroform the scoundrel." So, Paul begs him not to use the chloroform, promising to hold still. As the young surgeon continues probing, Paul realizes that he is simply tormenting him, for he looks up over his glasses to watch Paul's face. Finally, the surgeon tosses a piece of shell to Paul, saying, "Tomorrow you'll be off home." His leg is set in plaster and he takes a hospital train in the morning.
Kropp tells Paul that they must "work" the army medical sergeant so that they can stay together. They give the sergeant-major some cigars and promise more. "I understand," the sergeant says and they are allowed to stay together. On the train they ride to a hospital. At this hospital is a Dying Room where some men are taken, but one of them with a lung injury somehow survives and returns.  Unfortunately, Albert's leg is amputated and he is sent to a hospital where he will be fitted with a prosthetic. Paul is operated on because his leg will not heal from the setting. But, he does better after the operation, and is sent home to recuperate.