Ascorbic acid, commonly known as vitamin C, is a carbohydrate-like substance essential for certain metabolic processes in animals. Although most species are able to synthesize ascorbic acid within their bodies, humans do not have the capability and must ingest the vitamin as part of their diet. Featured below is a photomicrograph of ascorbic acid taken in polarized light.

Ascorbic Acid Specimen: Recrystallized ascorbic acid (vitamin C) Technique: Polarized Light

Because ascorbic acid is water-soluble, relatively large amounts are required by the body. The Recommended Daily Allowance (RDA) of ascorbic acid is 60 milligrams, which is a quantity sufficient to ward off the development of scurvy, a disease characterized by weakness, internal hemorrhaging, lesions, and loosening of the teeth. Many foods contain significant levels of ascorbic acid, particularly citrus fruits and tomatoes, but they should not be soaked or cooked in water if the nutrients are to be retained.

First isolated in 1928, ascorbic acid has since been the object of a considerable amount of research. Scientists have firmly established that the primary function of ascorbic acid is to assist in the production of the protein collagen. Moreover, ascorbic acid is an antioxidant and free radical scavenger, which some studies show to be an effective antiviral agent. Ascorbic acid has reportedly also been used in other capacities, such as aiding the healing of wounds, decreasing blood cholesterol levels, and reducing blood clotting, but little scientific evidence supports the substance's effectiveness in such cases.