Light micrograph (LM) of Vitamin C (ascorbic acid) crystals. Ascorbic acid is an organic acid found in citrus fruits and an antioxidant also known as vitamin C. Primates (including humans) and a few other species, such as the guinea pig, cannot synthesize vitamin C from glucose, resulting in the deficiency called scurvy. Ascorbic acid is a natural preservative. Magnification: x40 when shortest axis printed at 25 millimetres.