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The diagnosis of health is based on the shape, size and texture of the feces. So are the Egyptians, the Greeks and almost every ancient culture, even today your doctor may ask you when you last had a bowel movement – and to describe it in detail.
Of course it is uncomfortable to talk about it, but this is where science comes into play, because what we do Irritable bowel syndrome, inflammatory bowel disease, gastrointestinal infections and other pancreatic ailments bring Americans billions of dollars each year.
But as a researcher was trying to do this To contain problems, not our main motivation to find out some physics of defecation, it was something else, much more sinister.
When parenting strikes, it is hard n us is a working father who survived when he learned a number of new skills, one of which was the analysis of bowel movements. Years of diaper change and then potty training turned me from a poo analysis beginner into a crazy connoisseur. My life goes by in a series of pictures: hard feces like peas and long fecal matter like a smooth snake in a brown pool of water.
Unlike the ancients, we did not believe that we could predict the future of a stool. But we thought it was worth trying to understand where all these forms come from. Having a laboratory to answer questions from the everyday world is one of the special joys of being a scientist.
As fluent dynamic physicists, we partnered with colorectal surgeon Daniel Chu and two solid students, Candice Kaminski and Morgan LaMarca, to bring together defecation and hand-picked feces from 34 mammal species at Zoo Atlanta to measure their density and viscosity.
We've learned that most elephants and other herbivores produce "floaters," while most tigers and other carnivores produce "sinkers." We have also classified the feces from the most to the least odors, from tigers and rhinos to panda. The zoo's wildlife diversity offered us a range of faecal sizes and shapes, which served as independent evidence for the validation of our mathematical model for the duration of defecation.
We also added the feces to a device called a "rheometer". A precision mixer that can measure the properties of liquid-like and solids-like materials such as chocolate and shampoo. Our lab shares two rheometers with Georgia Tech physicist Alberto Fernandez-Nieves. Since then, we have categorized the rheometers as "clean rheometer" and "David Hu rheometer," which has seen its fair share of frog saliva, mucus, and fecal matter.
What else have we learned? Larger animals have longer faeces Larger animals defecate even at higher speeds: For example, an elephant at a speed of six centimeters per second performs almost six times as fast as a dog. The speed of defecation for humans is between two centimeters per second. Together, this meant that the duration of defecation across many species is constant (about 12 seconds (plus or minus 7 seconds)), although the volume varies greatly. If a bell curve distribution is assumed, 66 percent of the animals need between five and 19 seconds to determine the intestine. It's a surprisingly small range, considering that elephant dung at 10 milliliters has a volume of 20 liters, nearly a thousand times more than a dog , How can large animals excrete at such a high speed?
The answer we found was in th The properties of an ultrathin mucus layer lining the walls of the colon. The mucus layer is as thin as human hair, so thin that we could measure it only by weighing the feces while the mucus was evaporating. Despite its small thickness, the mucus is very slippery and more than 100 times less viscous than the faeces.
During stool, the faeces move like a solid plug. Under ideal conditions, the combined length and diameter of the faeces is therefore determined simply by the shape of the rectum and the colon. One of the great findings of our study was that feces extend from the rectum to half of the intestine.
If we summarize the length of the faeces with the properties of the mucus, we now have a coherent physics history for the occurrence of defecation. Larger animals have longer feces, but also thicker mucus, so that they can reach high speeds at the same pressure. Without this mucus layer defecation may not be possible. Mucus changes can contribute to various ailments, including chronic constipation and even bacterial infections such as C. difficile in the gastrointestinal tract.
Apart from our scientific curiosity, our measurements of feces have also found some practical applications. Our defecation data helped us design an adult diaper for astronauts. Astronauts want to stay in spacesuits for seven days, but are limited by diapers. We used the viscosity of the fecal matter and developed a diaper that separates the feces from direct skin contact. It was a semi-finalist of the NASA Space Poop Challenge earlier this year.
It just shows that physics and math can be used anywhere, even in your toilet bowl.
David Hu is Professor of Mechanical Engineering and Biology and Associate Professor of Physics at the Georgia Institute of Technology. Patricia Yang is a Ph.D. Student in Mechanical Engineering at the Georgia Institute of Technology.
This article has been re-published under the Creative Commons license of The Conversation. Read the original article.