人体每天需要一定数量的新鲜蔬菜,从蔬菜里摄取维生素丙、胡萝卜素和矿物质等,缺乏这些营养素,要发生种种疾病。在农村和城市中,蔬菜的供应十分充足,但是在边疆地区、丛山峻岭、沙漠地带或是拔海数千尺的高原上,获得蔬菜就非常不容易。再如北方有些地区,每到寒冬,蔬菜很少,人们往往感到新鲜蔬菜十分可贵。从这些事例中,我们便想到蔬菜的贮藏和运输问题。新鲜蔬菜中,含有百分之九十以上的水分和复杂的酵素,假使把它长途运输,既不经济,又容易腐烂;如果把水分和酵素除去,就可以长期保存,不致变质了。我们的祖先,早就发明了用干 Every day, the human body needs a certain amount of fresh vegetables. Vitamins C, carotene and minerals are taken from vegetables. In the absence of these nutrients, various diseases occur. In the countryside and in the cities, the supply of vegetables is abundant, but it is not easy to obtain vegetables in frontier areas, mountains, deserts, or thousands of feet above sea level. Another example is that in some areas in the north, there are few vegetables for each winter, and people often feel that fresh vegetables are very valuable. From these examples, we think about the storage and transportation of vegetables. Fresh vegetables contain more than 90% of water and complex enzymes. If they are transported on long distances, they are neither economical nor perishable. If water and enzymes are removed, they can be stored for a long time without deterioration. Our ancestors had long invented the use of dry