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Why Do Corpses Float?

I was reading this mystery novel last night, and in it this guy goes missing and then a week later they find his body floating in a nearby lake. I don’t get it–I have a hard enough time staying a float for ten minutes, and I’m alive. It’s a mystery how corpses do it.

Let’s see if we can figure this mystery out. The first clue is that the density of the human body is similar to the density of water, and what keeps us floating–other than the dog paddle–is the air in our lungs.

You’d think a corpse would sink as the air in its lungs is replaced by water. And they do–at least initially. But when any organism dies, it goes through putrefaction, the series of chemical, physical, and biological changes that end up returning the body to the food chain.

When a body dies, the bacteria that normally live in the digestive system continue to feed on the proteins and sugar in the body’s soft tissues, and to excrete gases including carbon dioxide, ammonia, hydrogen, and methane.

I give up! What does that have to do with floating?

Well, these gasses accumulate in the body’s cavities, and–if it’s submerged in water–eventually cause it to start rising.

Gross!

Decomposition happens more slowly in water, and even more slowly in cold water.

So the mystery solved!

昨晚，我讀了一本偵探小說，里面有個家伙失蹤了。一周后大家在附近的河面發(fā)現(xiàn)他的尸首。我不太明白。我一個大活人，要浮在水面十分鐘尚且不易，一具尸體為什么會浮起來呢?

我們來試著解讀奧秘吧!第一個線索是：人的身體密度近似于水的。人能浮于水面的關(guān)鍵在于肺部的空氣而不是靠在水中撲騰。

你可能認為，死者充滿空氣的肺部嗆入水后就會尸沉水下。確實如此，至少剛開始是這樣。任何生物體死后都難逃腐爛。腐爛需要經(jīng)歷化學(xué)反應(yīng)、物理變化和生理變化，最終的軀殼再回歸到食物鏈。

生物體死后，通常存在于消化系統(tǒng)的細菌繼續(xù)靠機體軟組織里的蛋白質(zhì)和糖分為生并釋放二氧化碳、氨氣、氫氣和甲烷等氣體。

我不猜了!這些和尸首浮于水面有什么聯(lián)系呢?

尸沉水下，這些氣體將匯集在體腔里，最終尸浮水面。

真惡心!