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“I know, too, that we must keep endless watch on ourselves lest in a careless moment we breathe in somebody’s face and fasten the infection on him. What’s natural is the microbe. All the rest—health, integrity, purity (if you like)—is a product of the human will, of a vigilance that must never falter. The good man, the man who infects hardly anyone, is the man who has the fewest lapses of attention. And it needs tremendous will-power, a never ending tension of the mind, to avoid such lapses.”