These inconveniences led to the adoption of what economists call a unit of value, that is, some article in which the worth of all other articles can be measured. Some particular commodity is selected which all will be willing to receive in exchange for their own goods, because thev know that they will be able later on to exchange it with someone else for another article. Any commodity which becomes an object of general desire, and which all are willing to accept as the medium of exchange, is rudimentary money. Any article may be selected as the unit of value, or common denominator, which acts as a medium of'exchange and forms the standard, or criterion, by which other commodities are valued. It is well known that at different stages of civilisation various articles have been adopted as the unit of value. Thus, in the hunting stage, skins are the usual form of currency. There is no doubt a refer ence to this in the Book of Job (ii, where we read.