Vivisection (from Latin vivus, meaning 'alive', and sectio, meaning 'cutting') is surgery conducted for experimental purposes on a living organism, typically animals with a central nervous system, to view living internal structure. The word is, more broadly, used as a pejorative catch-all term for experimentation on live animals by organizations opposed to animal experimentation but rarely used by practicing scientists. Human vivisection has been perpetrated as a form of torture.
Research requiring vivisection techniques that cannot be met through other means is often subject to an external ethics review in conception and implementation, and in many jurisdictions use of anesthesia is legally mandated for any surgery likely to cause pain to any vertebrate.
In the U.S., the Animal Welfare Act explicitly requires that any procedure that may cause pain use "tranquilizers, analgesics, and anesthetics", with exceptions when "scientifically necessary". The act does not define "scientific necessity" or regulate specific scientific procedures, but approval or rejection of individual techniques in each federally funded lab is determined on a case-by-case basis by the Institutional Animal Care and Use Committee, which contains at least one veterinarian, one scientist, one non-scientist, and one other individual from outside the university.
In the U.K., any experiment involving vivisection must be licensed by the Home Secretary. The Animals (Scientific Procedures) Act 1986 "expressly directs that, in determining whether to grant a licence for an experimental project, 'the Secretary of State shall weigh the likely adverse effects on the animals concerned against the benefit likely to accrue.'"