《太平广记·卷四百一十三·草木八》
那些进京去送的人，要成倍地给钱，因为在道上很容易被毒气薰着，薰着就头痛。
其赍致役夫，倍给其直，为其道路多为毒薰，以致头痛也。
The people who go to the capital city to deliver them have to be paid double, because along the way they are very likely to be exposed to the poison gas, and if they are exposed, they will get a headache.