The most horrific science experiments of all time - Many questionable scientific studies were performed for centuries until ethics groups were formed to restrict the types of experiments that could be carried out on live subjects. Fortunately, the fields of biomedicine and psychology have improved greatly when it comes to the types of experiments that can be done on humans and the importance of consent.

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Unit 731 - During World War II, the Japanese Army performed chemical and biological warfare experiments on Chinese, Korean and Mongolian natives.

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Unit 731 - The experiments included live weapons testing, germ warfare attacks, forced pregnancy, and vivisections performed without anesthesia.

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Unit 731 - General of the US Army Douglas MacArthur pardoned the Japanese doctors participating in these war crimes, saying that they were assisting America in biological warfare research.

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The Tuskegee Syphilis experiment - In Tuskegee, Alabama, United States, several hundred African-American male farmers who had contracted syphilis underwent a study of a drug they were told would cure their disease.

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The Tuskegee Syphilis experiment - However, even after penicillin was found to treat the disease, scientists denied the subjects the treatment as they wanted to observe the natural progression of the disease.

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The Tuskegee Syphilis experiment - By the end of the experiment, many of the men had died from the disease itself or related complications. The leaking of the event led to changes in consent laws for scientific experimentation in the US.

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Limb regeneration - Human limb regenerative powder was developed by the University of Pittsburgh's McGowan Institute of Regenerative Medicine in the United States.

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Limb regeneration - The catch is that the powder was developed from a pig's bladder, as detailed by the The Huffington Post. Apparently, the cells scraped from the bladder stimulate stem cells in the body to construct new tissue.

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Monkey despair - Psychologist Harry Harlow is well-known for his experiments on monkeys in the early 20th century. One experiment involved separating baby monkeys from their mothers to study clinical depression.

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Monkey despair - After they had bonded with their mothers, Harlow would place the monkeys in total isolation for 10 weeks. The monkeys became psychotic after a handful of days and were unable to be treated.

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Spider goat - At Utah State University, in the US, scientists genetically engineered goats that could produce milk containing the proteins found in spider silk.

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Spider goat - As spider silk is several times stronger than steel, the hope was that these new spider-goat hybrids could produce silk that would later be made into biosteel polymers and manufactured into things like artificial ligaments and tendons.

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Human-brained mouse - At the Salk Institute for Biological Studies in California, United States, researchers grew human brain cells out of stem cells injected into mice.

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Human-brained mouse - The human brain cells were found to successfully integrate into the developing nervous system of newborn mice, paving the way for future studies on new pharmaceutical therapies for neurodegenerative diseases, as outlined on Salk's website.

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The Emma Eckstein case - In the 1890s, the founder of psychoanalysis, Dr. Sigmund Freud, decided to treat his patient Emma Eckstein for what he determined to be hysteria and excessive masturbation.

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The Emma Eckstein case - He believed he could cure her by cauterizing her nose and had his surgeon-friend Wilhelm Fliess perform the surgery. She ended up developing a multitude of infections and was left permanently disfigured.

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Roman Emperor experiments - In medieval times, Holy Roman Emperor Frederick II was infamous for carrying out barbaric social experiments during his time in power.

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Roman Emperor experiments - In one experiment, he attempted to figure out if humans have a natural language by isolating newborn babies and not allowing them to have any social interaction. Instead of developing a language, they became savages and died in horrific conditions.

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Sex reassignment experiment - Psychologist and sex behavior expert Dr. John William Money had a theory that gender is learned rather than innate. He performed sexual reassignment surgery on a baby boy who was left without a penis after a failed circumcision.

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Sex reassignment experiment - The doctor convinced his parents to raise him as a girl, but the experiment failed when the child ended up identifying as male and not female.

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Removing body parts to cure insanity - Dr. Henry Cotton, a doctor at the New Jersey State Lunatic Asylum in the US, believed that diseased internal organs caused insanity.

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Removing body parts to cure insanity - In 1907, without getting consent from his patients first, the doctor extracted various body parts, including teeth and intestines, to study them.

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Removing body parts to cure insanity - Many of his patients ended up dying from the surgeries, which Dr. Cotton attributed to "end-stage psychosis," according to The New York Times.

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Electroshock therapy - Dr. Lauretta Bender of New York’s Creedmoor Hospital studied the effects of electroshock therapy on children in the 1960s.

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Electroshock therapy - She believed that it could be used to treat social issues and early signs of schizophrenia. She ended up applying the therapy to over 100 children before being forced to stop.

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Operation Midnight Climax - In the 1950s, the CIA sponsored a research project to study the effects of LSD and mind-altering chemicals.

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Operation Midnight Climax - Unsuspecting individuals were lured by prostitutes to a testing room where they were unknowingly given these substances and observed through a one-way glass.

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