Uric acid, also known as 2,6,8-trihydroxypurine, is a white crystalline compound, C5H4N4O3. Uric acid is the end product of protein metabolism in birds, invertebrates, and snakes, and of purine metabolsim in many insects, reptiles, birds, primates (including humans), and the Dalmation dog. It is the major form in which metabolic nitrogen is excreted (see also urea) . Being fairly insoluble, uric acid can be expelled in solid form, which conserves water in arid environments. The buildup of uric acid in the synovial fluid of joints causes gout.