It might not be the most impressive device on Franklin's resume, but his modification of the urinary catheter was no doubt a welcome relief for hundreds of Americans with bladder problems.
Then, as now, a catheter was a thin tube inserted into a patient's urethra in order to drain urine from the bladder. But at the time, catheters were nothing more than rigid (and painful) metal tubes. Franklin's older brother John suffered from kidney stones and needed to undergo an excruciating daily ritual of jamming a bulky metal catheter into his nether regions.
To make these daily attacks on his brother's loins less painful, Franklin ran to his local silversmith with plans for a flexible catheter. "It is as flexible as would be expected in a thing of the kind, and I imagine will readily comply with the turns of the passage," he wrote to John.