William Ashmore, Primary Lessons in Swatow Grammar…
“ But it may not be amiss for a learner to know that such a thing as slang not only exists, but that it is abundantly used. Every trade and occupation has its own slang best known to its own fraternity. In the market especially, trading operations are carried on between dealers and brokers by means of an extensive vocabulary of slang, used when occasion requires. Middle men who introduce a customer will conclude a bargain with the shop keeper about their own percentage, by the use of slang, in the presence of the country buyer himself who may not have the least idea of what is going on. ”
