Scurvy observed in any organism apart from humans and had been considered an exclusively human disease. Certain birds, mammals, and fish are susceptible to scurvy, but pigeons are unaffected, since they can synthesize ascorbic acid internally. Holst and Frølich found they could cure scurvy in guinea pigs with the addition of various fresh foods and extracts. This discovery of an animal experimental model for scurvy, which was made even before the essential idea of "vitamins" in foods had been put forward, has been called the single most important piece of vitamin C research. In 1915, New Zealand troops in the Gallipoli
Vitamin A deficiency bind with opsin. Night blindness results. Night blindness caused by VAD has been associated with the loss of goblet cells in the conjunctiva, a membrane covering the outer surface of the eye. Goblet cells are responsible for secretion of mucus, and their absence results in xerophthalmia, a condition where the eyes fail to produce tears. Dead epithelial and microbial cells accumulate on the conjunctiva and form debris that can lead to infection and possibly blindness. Decreasing night blindness requires the improvement of vitamin A status in at-risk populations. Supplements and fortification of food have been shown to be effective interventions.