(Bloomberg) -- The U.S. Senate imposes an ascetic existence on its members during an impeachment trial, but it does afford them one peculiar indulgence: milk.

Senators considering whether to remove President Donald Trump from office can drink either milk or water while in the chamber during the trial -- and nothing else, not even coffee. According to Senator Bill Cassidy, a physician and member of the Republican leadership, the little-known dairy exception was made decades ago to soothe lawmakers’ peptic ulcers.

“In the 50s, there was no medicine for ulcers but people would drink milk,” Cassidy says. “So the senators were allowed to drink milk because they had ulcers.”

No milk has been spotted thus far during Trump’s trial as House Democrats began to state their case on Wednesday. But the strict requirements on senators during the trial -- they must be present, silent and without electronic devices -- has put a spotlight on how they’re able to sustain themselves for hours on end on the Senate floor.

It’s unclear whether Cassidy’s explanation is true or lore. And if it’s true, modern medicine suggests it’s a misguided allowance: the calcium in milk actually causes the stomach to produce more acid, agitating an ulcer.

The Washington Post noted that while there isn’t a rule that explicitly allows milk, there also isn’t one that blocks it. The clearest articulation of the allowance is hidden deep within “Riddick’s Senate Procedures,” the Senate’s voluminous rulebook: “Senate rules do not prohibit a Senator from sipping milk during his speech.”

According to Senate records, the position on milk dates back to 1966, when Senator Everett Dirksen asked the presiding officer if it would be okay for a page to bring him a glass of milk. The officer answered there was no rule prohibiting him from requesting a glass of milk.

There’s one dietary luxury available to senators sitting through as many as 48 hours of argument: a bowl of candy. But by a mid-afternoon recess on Wednesday, an emergency loomed.

“The candy desk is running low. We need replenishments,” Senator Pat Toomey, a Pennsylvania Republican, reported.

--With assistance from Erik Wasson.

To contact the reporter on this story: Daniel Flatley in Washington at dflatley1@bloomberg.net

To contact the editors responsible for this story: Joe Sobczyk at jsobczyk@bloomberg.net, Joshua Gallu, Alex Wayne

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