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Why Do We Cry?

来源:中国数字科技馆

Why Do We Cry?

Source of pictures: Pixabay.com

Daniel was lying in the bed with eyes closed. But somehow he couldn’t fall asleep, as if there was a cartoon displaying in his mind and he couldn’t turn it off. He tried in vain many ways, such as wearing an eye mask, closing eyes and counting sheep, and drinking a glass of hot milk. The light in Mom and Dad's room was out. They were probably asleep. Daniel tossed and turned on the bed, thinking about how he fell asleep before. Suddenly, he remembered that he had once been criticized by the teacher for something, but he forgot what exactly it was. After came back home from the school, he felt wronged and cried himself to sleep on the bed. Later Mom came home and found Daniel in his room. Having seen his eyes as red as those of a rabbit, Mom made fun of him. Although it was a little embarrassing, he did sleep soundly that night. Daniel thought he got an idea. He thought hard about the past things he felt sad to force himself to cry. After several attempts, his eyes were finally tearful, and tears ran down his cheeks to the pillow. Soon he felt sleepy as his eyes were tired from crying. Then he fell asleep on the tear-soaked pillow.

The next day, Daniel was full of energy and shared his secret of falling asleep at breakfast with Mom and Dad. Cry ensured a deep sleep with sweet dreams. Dad heard and said, "You can fall asleep not because you're sleepy, but eyes get tired from crying and want to close."

Daniel answered in a casual tone, "Anyway, it made me sleep. I really couldn't sleep last night and wanted to ask you for help, but I figured out this idea and fell asleep." Mom said with interest, "I have heard tears can sterilize, protect the eyes, and relieve grief. But I didn't know it could help sleep." Daniel patted his chest proudly and said with absolute certainty, "It’s true. At least it worked for me. But what are the components of tears? Is there really something hypnotic?" He asked curiously. "As far as I know," Dad said while pouring milk, "tears are mostly composed of water, and have contain inorganic salts, grease, and some sticky proteins and proteins killing bacteria."

Mom nodded and continued, "Actually, there have been tears in our eyes and our eyeballs are like glass beads immersed in tears. The tear glands in our eyes secrete tears all the time, about a spoonful a day, to keep eyeballs moist. But when you are sad, the brain will instruct tear glands to tear continuously like a small fountain. Tears will flow out of the eye when it cannot hold so many tears."

Daniel said, "No wonder the eyes look watery. They are soaked in the water." Dad said suddenly. "In some cases, we can’t help crying." Daniel curiously asked, "Why?" Dad asked him on purpose, "What food do you hate most?" Daniel thought for a while and said, "I hate too many foods. Dad, which one are you talking about?"

Dad waved his hand around nose, frowned and said, "What’s this? Why does it smell like a fart?" Seeing dad were imitating Daniel when he saw an onion for the first time, Mom couldn’t help laughing, "That’s right, we can’t help crying while cutting onions." Daniel was puzzled and thought that it should be the onion to feel sad, not the person who cut it.

Mom laughed enough and then said, "Raw onions produce a substance called sulfenic acid. It stimulates the nerve endings when contacting with the cornea, so our eyes will feel tingle. Then the neurons send signals to tear glands, making it secret tears to wash the irritant out. Tears are precious and can protect our eyes. So don’t cry easily. It's too wasteful." 

Author: Huang Jing

本文来自:中国数字科技馆
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