During a particularly nasty outbreak of ague, a fever thought to be caused by malaria, Stone noticed that willow bark tasted an awful lot like Peruvian bark, the more common ague treatment of the time.
So he spent the next few years collecting, drying and powdering willow into a form that could be used to treat ague, eventually settling on a dosage of two scruples — which is a real unit of measure!
In addition to the pain and delay attendant on a broken limb, his exposure to the wet and cold had brought on fever and ague: which hung about him for many weeks, and reduced him sadly.