2. _Some kind of enjoyable good in general use comes to be money, that is, to be accepted as a medium of exchange._ The difficulties just mentioned are met by the use of a medium of exchange. A medium of exchange is simply one kind of wealth which is taken, not for itself, but to pass along, in the belief that it will enable the taker to gratify his wants and distribute his purchasing power in a more effective way. Money is an "invention" in that it is a means of exchange that came into use independently in a great number of communities. It is not an invention in the sense of a mechanical device suddenly hit upon, but rather in the sense of a social custom that grows as its convenience is tested by practice. Money is used, in some degree, everywhere except in the most primitive tribes. Historically viewed, the money first used in any community is seen in every case to be a commodity capable of giving immediate gratification, a direct good in immediate use. It then gradually comes to be used as money, which is an indirect agent. Still later, when the money habit is well established, a kind of material having no utility except as a medium of exchange may come to be used. [Sidenote: Qualities of the primitive money] 3. _Money in its origin is that good which best unites the qualities that make it easy to sell, to carry, to know, to keep, to divide, and unite._ It is evident that if some one commodity is gradually to take on this use as a medium of exchange there will be a choice; some things will be better fitted than others. First, this thing must have the quality of salability, or marketability. In the channels of exchange it is taken not because it is wanted for itself, but because it will help to get something else that is wanted. To be sure of a ready sale in a primitive community it must, however, be something that is generally desired. Food and clothing, which supply the fundamental physical needs, are the most generally used and desired of all goods. But they do not have the second quality of a good money material, that of great value in small bulk, transportability. Food is bulky. The carrying of a venison or of a bag of wheat on one's back a short distance requires an effort as great as that for the procuring of the food. Furs, however, have this quality in a high measure, united with other qualities of money, as is shown by their general use in the exchanges of northern tribes. Thirdly, a thing must be recognizable; counterfeits must be easily avoided, and the quality must be easy to test: this is the quality of cognizability. The love of ornament is universal in human societies, and gives value to many materials combining in a high degree the qualities thus far named. Fourthly, the money material, when taken in exchange, must remain without loss of quality, perhaps for long periods, until it can be exchanged again. Food does not answer to this requirement, being organic and perishable.