Many years ago, parents would use the “pickle test” to determine if a child had the mumps. Since the mumps causes the salivary glands to become tender and swollen, when someone with the mumps eats or drinks something acidic, the pain becomes worse. The theory was that if you give a pickle to a child with the mumps, you could tell that it was the mumps just by the look on their face! Never is this used now as a definitive test, because you never know how anyone will react when eating a pickle, especially a child!
I found this article in The Norwalk Hour out of Norwalk, Connecticut from December 26, 1925 called “The Pickles Test for Mumps is Scientific”:

If you can’t see to read it, here’s what it says:
“Here is how you can tell if you have the mumps, according to Dr. Beatrice R. Lovett, who writes about mumps in Hygeia. The earliest symptoms are stiffness and pain in the jaw, difficulty opening the mouth, and a drawing sensation after eating anything sour, hence the old fashioned test of eating a pickel. The mouth may be either unnaturally dry or filled with saliva. Within a day or two a swelling appears just below the ear, filling the space between it and the lower jaw. Usually one side swells first, and is followed in a few days by the other. The swelling increases rapidly, spreading forward and downward and giving the patient the unusual ‘mump-ish’ appearance of puffed our cheeks and neck. There is fever, usually not high, and a general feeling of discomfort and tension, although no actual pain in the swollen glands. Talking and eating are difficult because the patient is unable to open the mouth well, hence the name from the word mompen to mumble.”
The vaccine didn’t come until much later (1963), so unfortunately, during the time this article was written, lots of children came down with the mumps. My guess is that every doctor’s office had a nice big jar of pickles.