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The Science of Spit

This experiment comes from our cat, Mawra. She is a delightful cat, but when she is very happy, she drools. She was happily sitting in my lap while I was thinking of topics for this week's experiment. That's when it hit me. (Literally) Saliva! To learn more about spit, you will need:

  • a saltine cracker

If you don't have a plain saltine, you can use a piece of bread. First, rub all the salt off the cracker. We are trying to taste a very faint flavor, and the salt will overpower it.

Once you have removed the salt, put the cracker in your mouth and start chewing. Pay close attention to the taste. Very crackery, right? Now comes the hard part. Do not swallow the cracker. Just keep chewing and chewing. I found that it helps to pretend that it is chewing gum. Pay close attention to the flavor. After a minute or two of chewing, you should start to notice a slight sweet taste. The longer you chew it; the sweeter it will taste. It will not taste as sweet as candy by a long shot, but you should get enough sweetness to taste a little.

Why does the cracker begin to taste sweet? It has to do with your saliva. Saliva is the scientific term for spit, and it is very useful stuff. When you eat, your saliva moistens your food to help it go down easier, but it does more than just that. It contains an enzyme called amylase. Amylase changes the starch in your food into sugar. That is a good thing, because the starch molecules are too large to pass through the membrane around your cells. If it can't get into the cells of your body, it does not do you any good. Amylase breaks the starch molecules apart into molecules of glucose. Glucose is a kind of sugar, and its molecules are small enough to move through the cell membrane so your body can use it.

Saliva really is interesting stuff. It comes from salivary glands located in various parts of your mouth. It is about 99% water, with a little mucus to make it slippery and a trace of Amylase. Even that tiny trace of amylase can break down a lot of starch. If you have a jar of banana or sweet potato baby food, put a drop of saliva into the jar and put it into the refrigerator overnight. It needs to be a very starchy kind of food, not meat or green vegetables. By the next day, the baby food will be pretty much liquefied. The one drop of saliva digested the entire thing. Of course, you produce more than a few drops of saliva. The average person produces and swallows 1 to 1.5 liters of spit per day. Think about that while you eat another cracker.