One of the major leaps forward in gut science began with an accidental shooting at a trading post on June 6, 1822. A fur trader named Alexis St. Martin took a bullet in the abdomen, leaving him with a hole ripped through his muscle, bone and internal organs. Nobody expected him to survive. But he did. And the hole through his body survived, too.

In the process of healing, St. Martin’s skin knit itself together in such a way that he was left with a puckered opening under his breast that went all the way through to his stomach. His doctor, William Beaumont, could literally tie a bit of food on a string, shove it into St. Martin’s stomach through the hole, and pull it back out again. Using this one weird trick, Beaumont extracted samples of the man’s gastric juices. Over eight years and more than 200 awkwardly invasive experiments, St. Martin and Beaumont gave humanity its first real understanding of how digestion works and what happens inside the black box that is the gut.

It’s the first day of this week’s series on gut science. We’ve written about why we’re so obsessed with constipation and made a video about what poop can tell us about our health — and there’s more to come later in the week.

Today, scientists around the world are carrying on Beaumont’s groundbreaking work — only this time the path to knowledge lies through not the stomach, but the bowels. Scientists and the public at large are intensely focused on intestines, the processing of food that takes place in them, and the microbial communities that live and work in their depths. Federal spending on research related to the microbiome — the communities of microbes that live in you, animals and the natural environment — is rising. In fiscal year 2012, the U.S. government spent just more than $200 million on microbiome research projects. By 2014, that had risen to more than $450 million. And just last week the Obama administration announced the National Microbiome Initiative, a $121 million federal investment for “cross-ecosystem microbiome studies,” with additional cash from private agencies.

All of the new research promises to change our understanding of the strange alchemy that links the sandwich you ate for lunch with the teeming mass of symbiotic organisms living inside you. If we know more about that relationship, perhaps we can better diagnose your body’s systemic health.

This week, FiveThirtyEight’s science team will be separating fact from hype, doing a gut check on gut science. You can already learn about the history of constipation anxiety and what it can tell us about gut health. And there’s a video waiting for you about researchers in Canada who freeze-dry human poop. On Tuesday, you’ll discover how science’s bias toward Western cultures is helping to distort our understanding of what a “normal,” “healthy” gut ought to look like. On Wednesday, you’ll find out whether probiotics are worth a damn. And finally, on Thursday, you’ll dive into the surprising connections scientists are finding between your gut and your brain.

Our goal is to make the inner workings of your bowels as visible as that stray shot made the inner workings of Alexis St. Martin’s stomach. Come on, take a peek.