Water is so vital to us that it is easy to overlook that all but the smallest fraction of the water on Earth is poisonous to us—deadly poisonous—because of the salts within it.
水對我們太重要了，因此我們不容易注意到，地球上絕大部分的水對我們來說都是有毒的——而且毒得厲害，因為里面含有鹽。
We need salt to live, but only in very small amounts, and seawater contains way more— about seventy times more—salt than we can safely metabolize. A typical liter of seawater will contain only about 2.5 teaspoons of common salt—the kind we sprinkle on food—but much larger amounts of other elements, compounds, and other dissolved solids, which are collectively known as salts. The proportions of these salts and minerals in our tissues is uncannily similar to seawater—we sweat and cry seawater, as Margulis and Sagan have put it—but curiously we cannot tolerate them as an input.
有鹽我們才能活下去，但只要很小的量。海水里含鹽量太大——大了大約70倍——我們無法平安無事地將其新陳代謝。1升海水里只含有大約2.5茶匙普通的鹽——我們撒在食物上的那種鹽，但還含有大量的其他元素、化合物和別的已經溶解的團體，這一些通稱為鹽。鹽和礦物質在我們肌體組織里的比例，與在海水里的比例也差不多——正如馬吉利斯和薩根說的，我們出的汗是海水，流的泊是海水。但是，說來也怪，我們卻無法忍受外來的鹽。
Take a lot of salt into your body and your metabolism very quickly goes into crisis. From every cell, water molecules rush off like so many volunteer firemen to try to dilute and carry off the sudden intake of salt. This leaves the cells dangerously short of the water they need to carry out their normal functions. They become, in a word, dehydrated. In extreme situations, dehydration will lead to seizures, unconsciousness, and brain damage. Meanwhile, the overworked blood cells carry the salt to the kidneys, which eventually become overwhelmed and shut down. Without functioning kidneys you die. That is why we don't drink seawater.
要是把大量鹽攝人自己體內，你的新陳代謝很快會陷入危機。每個細胞里的水分子都會匆匆離去，像是許多志愿消防員急著要去稀釋和沖走突然增加的鹽分那樣。結果，細胞嚴重缺水、無法正常運轉。簡而言之，細胞脫水了。在極端情況下，脫水會造成疾病發作、昏迷和大腦損傷。與此同時，勞累過度的血細胞會把鹽輸送到肝臟，最后腎臟會負擔過重，停止運轉。要是腎臟不能正常運轉，你就會死去。這就是你不能飲用海水的原因。
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