I believe all of us are aware of this herb that is used in cooking but did you know that the roots could be used for medicine? In the Indian Household Medicine Guide ©1883, J.I. Lighthall wrote:
This is a garden plant, and the tops are used in cooking and flavoring different dishes, especially soups and dressing. The root is a splendid cooling diuretic, and should be given in all kidney troubles in low forms of fever. I have known it to succeed when more noted remedies failed. The only way I give it is in the form of a tea made from the green root, to be drank freely.
Household Medicine and sick-room © 1882 says:
Parsley.—The root and seeds of the garden parsley are unjustly neglected as domestic remedies. The dried roots taken in the form of a strong Infusion are useful diuretics in dropsies. The seeds, in doses of fifteen grains, simply bruised and swallowed, produce an effect somewhat similar to that of a glass of brandy-and-water. They cure intermittent*: in one experiment eighty-six cases of ague out of a hundred were so cured. Should be taken every four hours, in the intervals of the fits. The bruised leaves used as a poultice cure the bites or stings of insects. The seeds or leaves made into an ointment destroy vermin in the hair. A substance is separated from the seeds having the appearance of a fixed oil, and termed Apiol. It is a peculiar non-nitrogenous principle, powerfully antiperiodic, and is said to be almost equal to quinine The dose is five to seven drops every four hours. A saturated tincture of the seeds has proved a powerful remedy for intermittents.