In vitro (Latin: within the glass) refers to the technique of performing a given experiment in a controlle environment outside of a living organism; for example in a test tube. In vitro fertilization is a well-known example of this. Many experiments in cellular biology are conducted outside of organisms or cells; because the test conditions may not correspond to the conditions inside of the organism, this may lead to results that do not correspond to the situation that arises in a living organism. Consequently, such experimental results are often annotated with in vitro, in contradistinction with in vivo .