the 1890s he collaborated with Frederick Gowland Hopkins, a well-known and respected London physician and biochemist who studied the concept of how vitamins, then known as “accessory factors”, effect dietary health of patients. Under Hopkins's influence and led by his own childhood fascination with color variations, he took particular notice of how the color of urine changed. In 1897, a mother arrived at the Great Ormand Street Hospital with an infant and a diaper stained brownish-black. Dr. Garrod recorded the family history of the baby and kept tabs on the newborn's growth over the years. He quickly began seeking other patients with the same disorder and found forty cases and read up on the disorder, the first instance of which was noted in 1822. In 1900, the same mother became pregnant. Once the baby was born, Garrod had nurses closely inspecting the baby's diaper. Sure enough, they noted the appearance of the black urine 52 hours after the baby was born. Garrod subsequently deduced that the condition, alkaptonuria, was innate. Looking at his records, Garrod noticed that alkaptonuria was more likely to occur in the children of first cousins. Working with William Bateson, Garrod came to understand the pattern of alkaptonuria appearance in children based on Mendelian principles. Once he applied Mendel's concepts to alkaptonuria, he published a paper in 1902 called “The Incidence of Alkaptonuria: A Study of Chemical Individuality”. In the paper, Garrod explains how he came to understand the condition and speculates as to its causes. He cites various case studies and compares alkaptonuria to albinism in how it's inherited. In his paper, Garrod focuses on the concept of “chemical individuality” without any prior knowledge of what would come to be known as genes. He writes, “Owing, as I believe, to their chemical individuality different human beings differ widely in their liability to individual maladies, and to some extent in the signs and symptoms which they exhibit”. Alkaptonuria is a rare familial disease of organic acid metabolism that is best known for the darkening of urine from yellow to brown to black after it is exposed to the air. In later life, individuals with this disease develop arthritis characterized by deposition of brown pigment in joint cartilage and connective tissue. Garrod studied the recurrence patterns in several families, realized it followed an autosomal recessive pattern of inheritance, and postulated that it was caused by a mutation in