Vitamin B12 crystal structure model, 1957-1959.

UNITED KINGDOM - JULY 02: This crystal structure model, made for the X-ray crystallographer Dorothy Crowfoot Hodgkin, shows the structure of the hexacarbocylic acid fragment of Vitamin B12. It was displayed at the Brussels Universal Exhibition (�Expo�) in 1958. The full structure of this complex and large vitamin was determined by Hodgkin using X-ray crystallography in 1957, before chemists were able to work out using chemical means, and this model is a result of her work. Vitamin B12 is produced by micro-organisms in the gut. The richest natural source is raw liver. Deficiency leads to pernicious anaemia, which is the poor development of red blood cells resulting in the possible degeneration of the spinal chord. Sufferers develop extensive bruising and recover slowly from even minor injuries. (Photo by SSPL/Getty Images)