Obese mouse, 1998.
© Science Museum / Science & Society Picture Library
Taxidermal model of an obese mouse. At the end of a meal, fat cells send a chemical mesage to the brain giving out the signal that you are full and discouraging you from eating any more. Profesor Paul Trayhurn of the Rowett Research Institute in Aberdeen, Scotland, experimented on this mouse by 'knocking-out' the gene responsible for sending this signal. Consequently, the mouse did not know when to stop eating and became obese.