Urea: A nitrogen-containing substance normally cleared from the blood by the kidney into the urine. Diseases that compromise the function of the kidney often lead to increased blood levels of urea, as measured by the blood urea nitrogen (BUN) test.
Urea is of major historical significance. It was the first organic chemical compound ever synthesized. The German chemist Friedrich Wohler in 1828 attempted to make ammonium cyanate from silver cyanide and ammonium chloride and, in the process, accidentally made urea. Wohler wrote his mentor Jons Berzelius, "I must tell you that I can make urea without the use of kidneys, either man or dog. Ammonium cyanate is urea."
This pioneering experiment disproved the theory of vitalism, the concept that organic chemicals could only be modified chemically, but that living plants or animals were needed to produce them.
Wohler had also discovered that urea and ammonium cyanate had the same chemical formula but very different chemical properties. This was due to isomerism, the phenomenon in which two or more chemical compounds have the same number and type of atoms but, because those atoms are arranged differently, each compound has different chemical properties.