Foods that contain a substance called tryptophan, which is converted to an amino acid called L-tryptophan, promote sleep.

食物中含有一种称为色氨酸的物质，它可以转化为一种能促进睡眠的氨基酸—l -色氨酸。

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One substance gave him such hallucinations that he had to sleep them off for two days.

有种物质造成的幻觉极其强烈，以致他睡了两天才清醒过来。

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Dairy foods contain tryptophan, which is a sleep-promoting substance.

奶制品中含有的色氨酸是种有助增进睡眠的物质。

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The Emory researchers think this same sleep-inducing substance in spinal fluid may play a role in other conditions that involve excessive drowsiness.

WSJ: Unraveling the Riddle of Too Much Sleep