We often hear people say,"I have a good memory for things like that." or "I can remember names." But do you know memory is the single most important thing and it has played a very important part?For early men,there were dangers all around them--bad weather,wild animals.The keys to keep on living lay in man's ability to remember these dangers and the ways he had dealt with them in the past.And as man learned how to deal with them,he became civilized.Surprisingly,scientists have not yet found a way to open up the brain and observe its function without destroying it.Perhaps there are two types of memory:long-term and short-term.Short-term refers to those facts that stay with us for a few seconds to a few hours.For example,when you stay at a hotel,you remember the room number and forget it as soon as you leave.Long-term memory,on the other hand,means you remember things for a long period of time.If you spend your honeymoon in a special hotel,it's likely that you'll remember your stay quite clearly.Scientists also believe that a short-term memory can become a long-term memory if a lot of chemical and physical changes take place in the part of the brain.Although the human brain weighs three pounds,it contains 30 billion nerve cells acting like a computer.When those changes strengthen the links in certain nerve cells,a thought becomes a part of the long-term memory.