Quindlen links the conclusion to the introduction of her essay with the words "like many improbable ideas, when it works, it's a wonder", which is very close to her claim in the overall text, "America is an Improbable idea", it isn't supposed to work but it does despite all of the differences, specifically racial or ethnic, within it.
Answer: The author might be suggesting that the bacteria and diseases from the cesspool are leaking into their water source and into the shared water pump water, spreading the disease.
In this passage, Douglass does say he knows he left on a Saturday but did not know what day of the month or the year it was. He also knew terms of a ship because he used them the passage.
