Sentence:  Still [the rats] are an organized race, and can combine together for the purposes both of attack and defence; as the <WSD>nightmen</WSD> who clean the sewers and cesspools of Babylon often find. The travels of a <WSD>nightman</WSD> have never been published; but they would make a very curious book. As they worm their way along those dismal passages, they often find an army of rats drawn up to oppose their farther progress ... 
Meaning of the word marked with <WSD> tags:  A person whose job is cleaning cesspools or sewers, or emptying privies by night.