Read it through once

Soon all the laughers that were left were the owners and crews of boats that had two non-association pilots. But their triumph was not very long-lived. For this reason: It was a rigid rule of the association that its members should never, under any circumstances whatever, give information about the channel to any 'outsider.' By this time about half the boats had none but association pilots, and the other half had none but outsiders. At the first glance one would suppose that when it came to forbidding information about the river these two parties could play equally at that game; but this was not so. At every good-sized town from one end of the river to the other, there was a 'wharf-boat' to land at, instead of a wharf or a pier. Freight was stored in it for transportation; waiting passengers slept in its cabins. Upon each of these wharf-boats the association's officers placed a strong box fastened with a peculiar lock which was used in no other service but one--the United States mail service. It was the letter-bag lock, a sacred governmental thing. By dint of much beseeching the government had been persuaded to allow the association to use this lock. Every association man carried a key which would open these boxes. That key, or rather a peculiar way of holding it in the hand when its owner was asked for river information by a stranger--for the success of the St. Louis and New Orleans association had now bred tolerably thriving branches in a dozen neighboring steamboat trades--was the association man's sign and diploma of membership; and if the stranger did not respond by producing a similar key and holding it in a certain manner duly prescribed, his question was politely ignored.