translation.en: The bronchi branch, branch, branch and they stop branching, not because of any matter of principle, but because of physical considerations: the mucus, which is in the lung.
translation.zh: 支气管分枝，分枝，分枝。 它们停止产生分枝 不是因为规则的缘故， 而是因为物理的考虑—— 肺内的粘液。