Toxicology is "the study of the adverse effects of chemicals or physical agents on living organisms". Adverse effects may occur in lots of forms, ranging from immediate death to subtle changes not realized until months or years later. These substances may create toxic effects in living organisms as well as commotion in growth patterns, discomfort, disease and death. Knowledge of how toxic agents damage the body has progressed along with medical knowledge. It is now known that various visible changes in anatomy or body functions in fact result from previously unrecognized changes in exact biochemical in the body.