If Roger Waters hadn't gotten a stomachache in Philadelphia, the world might never have heard "Comfortably Numb."

When the Pink Floyd co-founder begins a three night run of his Us + Them tour at the Wells Fargo Center in South Philadelphia on Tuesday night, he'll be just across the street from where he was inspired to write one of his former band's most recognizable songs, which is certain to provide a climactic moment in his shows this week.

Here's the story, as Waters told it to me in 2010, when he also played three Wells Fargo shows, then as part of the Wall Live tour, in which he played the 1979 Pink Floyd double-album opus in its entirety.

" 'Comfortably Numb' resides in the Spectrum," he said of the sports and concert arena, which closed in 2009.

Here's why: Pink Floyd, which was formed in 1965 and which Waters recalled played Philadelphia "many, many times" starting in the late '60s, when they were habitues of the old Electric Factory when it was at 22nd and Arch, had a date at the Spectrum in South Philly on June 29, 1977.

"I was getting ready to do a gig there, and I had some stomach bug. Terrible, terrible stomach cramps," the 73-year-old bassist recalled. "We had a doctor come into the hotel and say, 'Well, we can take care of that.'

"And he gave me a shot, and to this day I don't know what it was. But it's not something I would ever recommend giving to a human being. It came out of a dart that felt like it was used to tranquilize an elephant. And we did the whole show, and I was barely able to stand. And that's where the term 'comfortably numb' came out of. Though obviously the song developed in a different direction."

Waters' ex-Floyd partner David Gilmour wrote the music for the song and plays a solo on it that guitar geeks consistently rank as one of the 100 best ever. In writing the lyrics, Waters used the memory of his hands' looking "way too big, frightening" during the Spectrum performance to point him toward a memory of being frightened and delirious as a boy: "When I was a child I had a fever / My hands felt just like two balloons."

And in his song about growing impervious to feeling in a cold, cruel alienating world, he paraphrased the dart-wielding Philadelphia doctor's words: "Just a little pinprick, there'll be no more, but you may feel a little sick," Waters, in the voice of his suffering alter ego Pink, sings. "That'll keep you going through the show, c'mon, its time to go."