The customs of this trade, which is learned and taught like any other, seem to vary little from country to country; although here and there one finds definite reasons why it should flourish a little more or a little less. When one part of a community is considered entirely subject to another part, or where one race is subject to another in the same country, this business seems to increase. Also military camps have always promoted it; the very conditions of camp life must give scope to it.