A.
An Indian boy ran swiftly from a village in Mexico. In his hand he carried a basket of fish. Only a few moments before, the fish had been pulled from the cold water of the lake. Farther on, another runner was waiting to take the basket from the tired boy and to race on. And so from one swift runner to another, fresh fish were rushed from the lake to the dinner table of Montezuma, ruler of the Aztecs. Speed is important in transporting fish and many other fresh foods. Foods that spoil easily must reach the market and the dinner table as quickly as possible. But now planes, trucks, trains, and ships have replaced runners. Planes are the fastest way to transport food. They are especially useful in carrying food to people and animals that could not be reached otherwise. Suppose there were a flood or an earthquake and the people could not be reached by trains or trucks. Unless packages of food could be dropped from planes, the people might starve. Trucks have many advantages. A truck can start as soon as it is loaded, and it can deliver goods directly to the market. Many modern trucks have their own refrigeration system. Today the tank truck that carries milk is a familiar sight on many country roads. The modern dairy farmer makes use of tank tracks that keep the milk fresh until it is delivered to stores and homes. Trains cannot always carry food as quickly as trucks. Many freight cars must be loaded before a train can start on a trip. And when the freight train arrives in the city, the food must be unloaded from the cars onto trucks to be taken to the market. All of this takes time. When railroad companies wanted to move perishable foods faster, they developed a plan that run on the rails. Some perishable foods can be transported by refrigerator ships. Bananas can be shipped in this way. They are loaded in the refrigerated hold of the ship while they are still green during the trip. As the green bananas are loaded, a man watches carefully for signs of yellow on them. If even one ripe banana is loaded, a whole shipload of fruit might be spoiled. But not all food needs to be moved as quickly or as carefully as perishable fresh food. Grains can make a slower trip without er of spoiling. Transportation by water is usually a cheap way of sending such foods. Trucks, trains, planes, and refrigerator ships are modern ways of transporting food. But a great deal of food is still carried on the heads of women and on the backs of animals. Over the desert sands, camels carry loads of salt, dates, and cheese.