Spit. Slobber. Dribble. Drool.
The words do sound gross. Yet saliva – a substance that’s 98% water – is totally important to your dental and digestive health. Its main roles include
- Kicking off the digestive process, as enzymes in the saliva start to break down the food we eat.
- Washing away food particles, as well as bacteria and other oral microbes that can cause decay.
- Keeping the gums, tongue and other soft oral tissues moist and protected.
But there’s one thing saliva can do that we’ve never really understood until just recently: form beads – as it will do if you put a bit of saliva between two fingertips and slowly pull them apart.
Why should it act this way when other polymer-containing fluids don’t? (A polymer is a compound that has large molecules made of many small, simple and repeated units. Some other common natural polymers are cellulose, rubber and shellac.)
According to a Futurity.com report on research recently published in Nature Physics,
a key factor in the beading mechanism is fluid inertia, or the tendency of a fluid to keep moving unless acted upon by an external force.
Other major elements are a fluid’s viscosity; the time it takes a stretched polymer molecule to “relax,” or snap back to its original shape when stretching is stopped; and the “capillary time,” or how long it would take for the surface of the fluid strand to vibrate if plucked.
“It turns out that the inertia has to be large enough and the relaxation time has to be small enough to form beads,” Bhat says.
Here are a few more interesting facts about saliva:
- We don’t salivate very much at all when we sleep, but while we’re awake, the three salivary glands secrete about a pint and a half of saliva daily.
- We wouldn’t be able to taste food without saliva.
- Although saliva is mostly water, it also contains important elements such as electrolytes, enzymes, epidermal growth factor (a substance that helps regulate cell growth), antibacterial compounds and opiorphin (a pain-killing compound). Some of these can tell us a lot about a person’s health through simple, non-invasive testing.
- Saliva’s boiling point is three times greater than that of water.
- In some animals, saliva can help heal wounds through the presence of a protein called nerve growth factor that’s applied when the animals lick their wounds.
- Saliva has an anti-fog effect, which is why you sometimes see swimmers or divers smearing spit on their goggles.