Imagine for a moment the year 1800. A doctor is meeting with a patient – most likely in the patient’s home. The patient is complaining about shortness of breath. A cough, a fever. The doctor might check the patient’s pulse or feel their belly, but unlike today, what’s happening inside of the patient’s body is basically unknowable. There’s no MRI. No X-rays. The living body is like a black box that can’t be opened.

The only way for a doctor to figure out what was wrong with a patient was to ask them, and as a result patients’ accounts of their symptoms were seen as diseases in themselves. While today a fever is seen as a symptom of some underlying disease like the flu, back then the fever was essentially regarded as the disease itself.

But in the early 1800s, an invention came along that changed everything. Suddenly the doctor could clearly hear what was happening inside the body. The heart, the lungs, the breath. This revolutionary device was the stethoscope.