你每天都早晚刷牙吗？是不是清洁后，口腔就会干净了呢？事实可不是这样，我们的口腔中住着大批的“居民”呢，一起来认识一下吧！

YOUR MOUTH IS A JUNGLE!

For the bacteria, fungi, protozoa, and viruses inhabiting our mouths, life is a piece of cake, or whatever else we have eaten. What we lunch on, they munch on.

In fact, our mouths are ecosystems for them, as the weather forecast remains the same at 95? F, unless we are ill, the level of humidity at 100%, and the guaranteed a free meal on, actually in, the mouth is unconditional. They select their own living quarters, with some preferring life between the teeth, others preferring the space between the gums and the teeth, others preferring the roof of the mouth, and yet others preferring the cracks in the front or in the back of the tongue. They do, however, work for this luxurious lifestyle, by performing such tasks as eating each other, fending off bad species of bacteria, etc., manufacturing different products, and eating the food that becomes lodged in parts of our mouths.

The only harmful species of bacteria inhabiting our mouths is Streptococcus mutants, the cavity causing bacteria. Microbiologists believe that initially, this bacteria was our friend, and played a useful role in our mouths, just as the other species of bacteria do. As man progressed down the evolutionary timeline and began refining raw sugar, Streptococcus mutants became the enemy. This species thrives upon refined sugar and, as a part of its digestive process, converts sugar into acid.

Before man began refining sugar, the bicarbonate ions in our saliva possessed the ability to counteract the acid it produced. With the arrival of refined sugar on the scene, and Streptococcus mutants' insatiable appetite for it, acid production increased to the point where the saliva could no longer counteract it. The excess acid produced erodes our teeth, causes cavities, and subsequent visits to the dentist.

The more than 100 species of bacteria, and hundreds of species of fungi, protozoa, and viruses that have taken up residence in our mouths is difficult to fathom. Microbiologists estimate that, in addition to these known species, there are up to 500 other living, breathing organisms inhabiting our mouths, although only 50 have been identified and named. The sheer number of these creatures is astronomical, considering the fact that our mouths contain more bacteria than the entire world's population, and the fact that our bodies house approximately one trillion bacteria.

What is a person to do about these squatters? Nothing. Our bodies provide an ecosystem for them and, in return, they defend us from the invasion of bad bacteria, viruses, fungi, and protozoa, with the exception of Streptococcus mutants and a couple of other undesirable species.

Our dentists' advice to brush and to floss our teeth on a regular basis should be taken, as doing so helps to maintain healthy levels of these creatures from between 1,000 to 100,000 per tooth.

Enjoy your next meal... they certainly will!

（来源：coolquiz.com 英语点津Annabel编辑）