6 inch Kidney Stones!!!
Kidney stones are known technically as renal calculi, and are formed when materials dissolved in the urine precipitate out in the pelvis of the kidneys (or ureters) to form solid crystalline lumps. They are usually formed of calcium oxalate, uric acid or calcium phosphate. These stones can be extremely painful and can block the internal flow of urine as well as producing blood and puss in the urine (haematuria and pyuria respectively).
There seems to be a range of possible causes of kidney stones including amongst other things: ongoing dehydration, ingestion of large amounts of oxalate (e.g. chocolate, nuts, soya beans, rhubarb and spinach), a high protein diet and hyperthyroidism.
Famous scientists who have suffered from kidney stones include: Sir Isaac Newton (opposite), Robert Boyle, Nicholas Steno and William Harvey!