Today, scientific experiments are controlled by a number of regulatory bodies that ensure a certain standard of ethics in any study or test, but this system has not always been around to protect both human and animal test subjects.

Here is a look at the most gruesome and horrifying inhumane science experiments throughout history.

Sigmund Freud and the case of Emma Eckstein

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Emma Eckstein was one of Sigmund Freud's most important patients, providing him with a number of insights into the (now outdated) study of hysteria. She was also subject to a number of disturbing medical experiments, courtesy of Freud's friend, Willhelm Fleis, a surgeon who believed hysteria could be treated by cauterizing the nose. The operations on Eckstein were disastrous, leaving her permanently disfigured, and causing a number of infections.

Nazi Experiments

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Likely the most infamous case of inhumane experimentation in history was that carried out by the Nazis during the Holocaust. Prisoners of concentration camps, mainly Jews, were subjected to a wide range of horrifying experiments, testing transplantation techniques, studies of injuries or exposure to dangerous substances, disease experiments, and tests of chemical weapons. The experiments were often based on the Nazi's flaw racial ideology, and are generally considered to have produced little to no valuable results, even disregarding their status as medical torture.

Unit 731

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Unit 731 was the Japanese counterpart to the Nazi's human experimentation, and was a covert biological and chemical warfare research and development unit of the Imperial Japanese Army that conducted lethal human tests on Chinese prisoners and populations during the Japanese occupation of China during World War II. Between 3,000 and 12,000 men, women, and children were killed in the tests of bio-warfare, vivisection, and experiments involving rape and forced syphilis infection.

Poison Laboratory of the Soviet Secret Services

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Throughout a large part of its history, the Soviet Secret Services maintained a secret and illegal laboratory dedicated to developing poisons to be used in political assassinations. Many of the chemicals, including mustard gas, ricin, digitoxin, and curare, were tested on prisoners of the Soviet Union's extensive gulag system, with an unknown number being killed. A number of poisons developed by the program were then provided to the KGB, and were used in assassinations of figures throughout Europe.

Project MKUltra

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Project MKUltra was the code name given to an illegal program of experiments on human subjects, designed and undertaken by the CIA from the 50s until the 70s. The program focused on producing drugs and procedures to be used in interrogations and torture, as well as to investigate the possibility of mind-control. MKUltra used numerous methodologies to manipulate the mental states of some 149 subjects at prisons, hospitals, and universities using drugs such as LSD, hypnosis, sensory deprivation, isolation, verbal and sexual abuse, as well as various forms of torture.

Project 4.1

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Project 4.1 was a medical study conducted by the United States of those residents of the Marshall Islands exposed to radioactive fallout from the March 1, 1954 Castle Bravo nuclear test at Bikini Atoll. The government maintains that the exposure was accidental, but they nevertheless never obtained informed consent from the study subjects, many of whom suffered as a result of the later medical experimentation.

Pit of Despair

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In the 1970s, American comparative psychologist Harry Harlow conducted experiments on rhesus macaque monkeys at the University of Wisconsin–Madison, looking to produce an animal model of clinical depression. The device Harlow created was named (by him) the "Pit of Despair" and consisted of an isolation chamber into which monkeys between three months and three years old would be placed alone, after they had bonded with their mothers, for up to ten weeks. After a few days, the monkeys stopped moving about and remained huddled in a corner. Harlow's experiments were largely condemned.

Two-Headed Dog Experiment

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In the 1950s, Soviet scientist and organ transplant pioneer Vladimir Demikhov conducted a number of experiments on animals, including transplantation of the heads of dogs, producing a number of two-headed dogs. The dogs did not survive the procedure, but the research went on to inspire similar experiments, such as the head transplants in monkeys by Dr. Robert White.

Tuskegee Syphilis Experiment

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The Tuskegee syphilis experiment was a clinical study conducted between 1932 and 1972 by the U.S. Public Health Service to study the natural progression of untreated syphilis, particularly among rural African-American men in Alabama. During the study, the men were led to believe they were receiving free healthcare from the government. Over the course of the study, 600 men were enrolled in the study, hundreds of whom were diagnosed with syphilis, but intentionally left untreated. Numerous victims died of the the disease, and it was subsequently spread to a number of other people. A leak exposed the program in 1972, leading to a series of Congressional hearings and greater regulation of government studies.

The Aversion Project

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Between 1971 and 1989, the South African government conducted an aversion therapy medical program which attempted to cure gays and lesbians of homosexuality. Headed by Professor Aubrey Levin, the program targeted individuals in the military, and victims were submitted to chemical castrations and electric shock treatment, meant to cure them of their homosexual “condition.” Around 900 homosexuals who were drafted into the military were forced to undergo “sexual reassignment” surgeries against their will, and then turned out into the general public, often with their procedures unfinished, and without any medical aid or support.