I first came across one of medicine’s most ubiquitous but uncelebrated tools at the rural GP practice where I interned as a student. Now and then a patient would object to my presence and I’d be sent to wait in the corridor. Lingering outside the door seemed shifty, so I’d go to the staffroom and do the washing-up. (“Isn’t the new student helpful?” I liked to imagine them saying.) One day I was rinsing a mug when I noticed it was decorated with little pictures of turds. Imagine choosing to drink out of a cup patterned with faeces, I thought. Doctors are so odd.

I didn’t know at the time that I was washing up a representation of the Bristol stool chart. The BSC is known to everyone in medicine, a remarkable piece of categorisation that’s useful for both comedy and clinical practice. (Alas for Bristol, you can’t dictate your preferred reasons for medical fame: see also the “Liverpool Care Pathway”.) It was devised in the 1990s by Dr Kenneth Heaton, a leading researcher into irritable bowel syndrome, who died last year.

Dr Heaton was interested in gut transit time: how long it takes food to pass through the digestive system. He theorised that the shapes that emerged signalled the time they’d taken to form, which led him to formulate a series of verbal descriptions called the Bristol stool form scale, later illustrated as the Bristol stool chart. “It was easy pickings,” he once said. “It’s an extraordinarily under-researched area. Processing stools in a laboratory does not appeal to everyone.”

The chart runs from Type 1 (constipated, or “Separate hard lumps, like nuts”) to Type 7 (frank diarrhoea) via explicitly annotated stages. Type 4, for example, is “Like a sausage or a snake, smooth and soft.” (“The perfect stool!” sighed our gastroenterology registrar. “Of course, there’s no such thing as ‘perfect’ – it’s what’s normal for the individual,” he added, caressing the Type 4 diagram in a way that compromised his sincerity.)

The Bristol stool chart is all over the internet, in most hospitals and doctors’ surgeries, and now, inevitably, available as an iPhone app.

Despite this, there’s something anachronistic about it. The chart belongs to a disappearing world of purely clinical medicine, where – in the absence of tools for imaging and investigation – description and observation counted for everything. Ancient and medieval physicians scrutinised, described what they saw, then codified their findings in an attempt to formulate diagnoses.

Contemporary medicine can sometimes seem a whirl of powerful drugs and big machines – with the contribution of this kind of careful attention to small things too often overlooked. But without language to describe what you’re seeing, you can’t always know if you’ve made a problem better; and research is difficult if you can’t express your findings, or compare one outcome with another.

Because the subject is traditionally embarrassing, it can also be hard to treat people who are suffering from bowel problems. They may find it easier to point to a piece of paper (or a GP’s coffee mug) than embark on a detailed account of their last trip to the lavatory.

I only wish there was an appendix to the scale that would allow patients to tell us about the presence of blood: “PB” for blood seen on the paper or in the bowl, say; “M” if it’s mixed in with the stool. It might be nothing, it might be something – and that something might be eminently treatable. But if you consider it unmentionable, no one will be able to find out.

Sophie Harrison is a hospital doctor in South Yorkshire. This column appears fortnightly

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