“Oh, come along,” Joachim said. “I can explain it to you as we go. You looked rooted to the spot! It’s a surgical operation, they often perform it up here. Behrens is a regular dab at it. When one of the lungs is very much affected, you understand, and the other one fairly healthy, they make the bad one stop functioning for a while, to give it a rest. That is to say, they make an incision here, somewhere on the side, I don’t know the precise place, but Behrens has it down fine. Then they fill you up with gas⁠—nitrogen, you know⁠—and that puts the cheesy part of the lung out of operation. The gas doesn’t last long, of course; it has to be renewed every two weeks; they fill you up again, as it were. Now, if that keeps on a year or two, and all goes well, the lung gets healed. Not always, of course; it’s a risky business. But they say they have had a good deal of success with it. Those people you saw just now all have it. That was Frau Iltis, with the freckles, and the thin, pale one was Fräulein Levi, that had to lie so long in bed, you know. They have formed a group, for of course a thing like the pneumothorax brings people together. They call themselves the Half-Lung Club; everybody knows them by that name. And Hermine Kleefeld is the pride of the club, because she can whistle with hers.