We all know how the journey through the digestive（消化的） system ends, but few give much thought to how it begins. If the mouth is the doorway（门口）, saliva is the greeter. One of the most important substances produced by the body, yet（但是） one of the most overlooked（忽略）. And to many, one of the grossest（总的）, conjuring（ 召唤） up words like "*beep*". What did I say? *beep* I can't.

  M-O-I-S-T. I can't say *beep*. Alright, fine then. Let's move on in moist（湿润的）. Perhaps the best way to really appreciate saliva is to learn what it'd be like to live without it. I give you the time-honored（纪念） scientific tradition of the salt challenge.

  Six crackers, no water, one minute on the clock. I can't swallow（ 吞下）, it's not even in my mouth. To make saliva, cells（细胞） pump（用抽机抽） out salts and because of osmosis, that draws out water. Unlike with tears（ 眼泪） or sweat, that salt is then taken back up by the gland（[解剖]腺）, leaving it with something that's about 99% water. The other 1% is proteins（蛋白质） and other molecules which give saliva that sticky（粘的） feel（感觉）, you know, and, well, have feelings about. But that 1% is also where most of the cool spit happens.

  But not all saliva is secreted（隐秘） equal. We pump out two different brands of mouth juice. Unstimulated saliva is secreted by hundreds of tiny glands all over our mouth. And we make it essentially（ 本质上） all the time. This saliva contains a special ingredient called mucin, which is a protein that loves to soak（浸） up water, creating a kind of gel（[物化] 凝胶） that forms a thin protective（保护的） coating（被覆） all over your mouth parts. Mucin is basically（基本上） why saliva sounds like this.

  On the other gland, stimulated（刺激） saliva is, well, what it sounds like.