A very soluble crystalline body which is the chief constituent of the urine in mammals and some other animals. It is also present in small quantity in blood, serous fluids, lymph, the liver, etc. [1913 Webster
" It is the main product of the regressive metamorphosis (katabolism) of proteid matter in the body, and is excreted daily to the amount of about 500 grains by a man of average weight. Chemically it is carbamide, CO(NH2)2, and when heated with strong acids or alkalies is decomposed into carbonic acid and ammonia. It unites with acids to form salts, as nitrate of urea, and it can be made synthetically from ammonium cyanate, with which it is isomeric."