Arginine liquid and bubbles, differential interference contrast light micrograph. Here, this chemical has been heated and melted to form a viscous liquid that has pooled around air bubbles. Arginine is a semi-essential amino acid. The L-form, seen here, is one of the 20 most common natural amino acids. It can be synthesized by the body and so does not need to come from the diet. Arginine is involved in the production of urea, the principal form in which mammals excrete nitrogenous compounds from the body, and also plays a role in wound healing and cell division. Magnification: x25 when printed at 10 centimetres wide.