In his best-selling book Folk Medicine, Dr. D.C. Jarvis, an authority on old Vermont folk remedies, described an extraordinary experiment. He asked twenty-four people to keep a daily record of the food they ate for two years. They were to check the acid-alkaline reaction of their urine each day using a simple litmus-paper test. Comparing his patients' medical records with their urine tests, Jarvis saw a clear pattern. A few days before the onset of an illness, a patient's urine shifted from acid to alkaline.

The alkaline reaction usually corresponded with eating specific foods. Jarvis was surprised to learn that one of Vermont's oldest and most popular tonic drinks, two teaspoons of apple cider vinegar and a teaspoon of honey in a cup of water, shifted the urine reaction back to a healthy acidic condition. Old timers, as Jarvis discovered, used vinegar for chronic fatigue, headache, high blood pressure, dizziness, sore throat, obesity, and a host of other ailments that afflicted both humans and farm animals.

Medical researchers now believe it is the amino acids present in vinegar that are partly responsible for its medicinal effects. In particular, these amino acids help counter the effects of lactic-acid buildup in the blood, which can cause fatigue; irritability; stiff, sore muscles; and can contribute to disease.

However, for the stouthearted, the following old Japanese tonic is said to be very effective for increasing stamina and maintaining general health. Wash an egg, being careful not to break the shell. Immerse the egg in a cup of brown rice vinegar for two to three days, or until the shell dissolves leaving the inner soft skin. Discard the skin and mix the egg and vinegar well. Drink a sake cup of this liquid three times a day (after meals). Known as tamago-su (egg-vinegar drink), this is one of Japan's most potent folk remedies.