Mark "Rent-boy" Renton: Now I've justified this to myself in all sorts of ways. It wasn't a big deal, just a minor betrayal. Or we'd outgrown each other, you know, that sort of thing. But let's face it, I ripped them off - my so called mates. But Begbie, I couldn't give a shit about him. And Sick Boy, well he'd done the same to me, if he'd only thought of it first. And Spud, well okay, I felt sorry for Spud - he never hurt anybody. So why did I do it? I could offer a million answers - all false. The truth is that I'm a bad person. But, that's gonna change - I'm going to change. This is the last of that sort of thing. Now I'm cleaning up and I'm moving on, going straight and choosing life. I'm looking forward to it already. I'm gonna be just like you. The job, the family, the fucking big television. The washing machine, the car, the compact disc and electric tin opener, good health, low cholesterol, dental insurance, mortgage, starter home, leisure wear, luggage, three piece suite, DIY, game shows, junk food, children, walks in the park, nine to five, good at golf, washing the car, choice of sweaters, family Christmas, indexed pension, tax exemption, clearing gutters, getting by, looking ahead, the day you die.
Mark "Rent-boy" Renton: Never again, Swanney. I'm off the scag.
Swanney: Are you serious?
Mark "Rent-boy" Renton: Yeah, no more. I'm finished with that shite.
Swanney: Well, it's up to you, man.
Mark "Rent-boy" Renton: Gonna get it right this time. Gonna get it sorted out. Gonna get off it for good.
Swanney: I've heard that one before.
Mark "Rent-boy" Renton: The Sick Boy method?
Swanney: Well, it nearly worked for him, hey.
Mark "Rent-boy" Renton: Well, he's always been lacking in moral fiber.
Swanney: He knows a lot about Sean Connery.
Mark "Rent-boy" Renton: That's hardly a substitute.
Mark "Rent-boy" Renton: Take the best orgasm you've ever had... Multiply it by a thousand, and you're still nowhere near it.
Allison: It beats any meat injection. That beats any fucking cock in the world.
Sick Boy: Personality, I mean that's what counts, right? That's what keeps a relationship going through the years. Like heroin, I mean heroin's got a great fucking personality.
Mark "Rent-boy" Renton: We took morphine, diamorphine, cyclizine, codeine, temazepam, nitrazepam, phenobarbitone, sodium amytal, dextropropoxyphene, methadone, nalbuphine, pethidine, pentazocine, buprenorphine, dextromoramide, chlormethiazole. The streets are awash with drugs you can have for unhappiness and pain, and we took them all. Fuck it, we would have injected vitamin C if only they'd made it illegal.
Tommy: Doesn't it make you proud to be Scottish?
Mark "Rent-boy" Renton: It's SHITE being Scottish! We're the lowest of the low. The scum of the fucking Earth! The most wretched, miserable, servile, pathetic trash that was ever shat into civilization. Some hate the English. I don't. They're just wankers. We, on the other hand, are COLONIZED by wankers. Can't even find a decent culture to be colonized BY. We're ruled by effete arseholes. It's a SHITE state of affairs to be in, Tommy, and ALL the fresh air in the world won't make any fucking difference.
Mark "Rent-boy" Renton: Choose Life. Choose a job. Choose a career. Choose a family. Choose a fucking big television, choose washing machines, cars, compact disc players and electrical tin openers. Choose good health, low cholesterol, and dental insurance. Choose fixed interest mortgage repayments. Choose a starter home. Choose your friends. Choose leisurewear and matching luggage. Choose a three-piece suit on hire purchase in a range of fucking fabrics. Choose DIY and wondering who the fuck you are on Sunday morning. Choose sitting on that couch watching mind-numbing, spirit-crushing game shows, stuffing fucking junk food into your mouth. Choose rotting away at the end of it all, pissing your last in a miserable home, nothing more than an embarrassment to the selfish, fucked up brats you spawned to replace yourselves. Choose your future. Choose life... But why would I want to do a thing like that? I chose not to choose life. I chose somethin' else. And the reasons? There are no reasons. Who needs reasons when you've got heroin?
Answer: The generally-accepted answer is that the baby starved to death. This information comes from the novel and isn't explicitly stated in the film. In the book, it is due to neglect (starvation or dehydration) because of the parents' heavy drug use.