题目内容：
Aristotle, the Greek philosopher, summed up the four chief qualities of money 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 pieces 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 .A traveler there might starve if he had none of the particular ‘ local money ’. Among isolated peoples ,who are not often reached by traders from outside ,commerce usually means barter ,which is a direct exchange of goods .Perhaps it is fish for vegetables or meat for baskets .For this kind of simple trading, money is not needed ,but there is often something that everyone wants ,such as salt to flavor food, shells for necklaces ,or iron and copper to make into tools. 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 material to use as money ,but in countries where the food of
the people is mainly vegetables ,it is often an absolute necessity .Cakes of salt ,stamped to show
their value ,were used as money in Tibet until recent times, and they can still buy goods in parts of Africa.
Cowrie seashells have been used as money at some time or another over the greater part of the Old World. These were collected
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