Aristotle, the Greek philosopher, summed up the four brief qualities of money some 2 000 years ago. It must be lasting and easy to recognize, to divide, and to carry about. When we think of money today, we picture it either as round, flat piece of metal which we call coins, or as printed paper notes. But there are still parts of the world today where coins and notes are of no use. They will buy nothing, and a traveler might starve if he had none of the particular local 'money' to exchange for food. Among isolated peoples, who are not often reached by traders from outside, commerce usually means barter. There is direct exchange of goods. Perhaps it is fish for vegetables, or meat for grain. For this kind of simple trading money is not needed, but there is often something that everyone wants and everybody can use, such as salt to flavor food, shells for ornament, or iron and copper to make tools and vessels. These things—salt, shells or metals—are still used as money in out-of-the-way parts of the world today. Salt may seem rather a strange substance to use as money, but in countries where the food of the people is mainly vegetable, it is often an absolute necessity. Cakes of salt, stamped to show their value, were used as money in Tibet until recent times, and cakes of salt will still buy goods in Borneo and parts of Africa. Sea shells have been used as money at some time or another over the greater part of the Old World. Metal, valued by weight, preceded coins in many parts of the world. Nowadays, coins and notes have replaced nearly all of the picturesque (独特的) form. of money, and although in one or two of the remote countries people still store it for future use on ceremonial occasions such as weddings and funerals, examples of primitive money will soon be found in museums. The following are qualities of money summed up by Aristotle EXCEPT______.