WARNING: Graphic pictures
Kittens have had their skulls broken, electrodes attached to their brains, ribs and spines and been left paralysed as a result of experiments carried out at universities across the world.
Universities in the UK experimented on the felines, often paralysing them and collapsing their lungs in order to discover more about the human body, animal charity PETA has revealed.
The universities include Cardiff, University College London and Cambridge.
PETA revealed that the cats endured a variety of experiments, including having their eyes stitched shut so that scientists could analyse the causes of a lazy eye.
The animal charity also stated that scientists collapsed the cats lungs, while other cats were injected with paralysing drugs to prevent them from being able to move and breathe.
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Most of the cats and kittens were killed following the experiments.
Story continues below gallery. HuffPost has decided not to publish the most extreme images
PETA spokesperson, Ben Williamson, said: "Experimenting on cats and dogs who would normally share our homes can never be justified, and we fully support the proposed ban that would end their use in laboratories.
"The development of cutting-edge, non-animal methodologies that accurately predict what will happen in human beings is exciting and progressive, and unless University College London wishes to be at the bottom of the class, it should embrace today's humane research breakthroughs. Its students, researchers and teachers would benefit from modernisation, and animals would not have to endure traumatic and fatal experiments."
PETA revealed that experiments at Cardiff University showed that kittens were raised in darkness or had their eyelids sewn shut, and were then subjected to brain experiments and killed.
A total of 31 kittens and their mothers in some cases were used in the research which took place in 2010 but has only recently come to light.
PETA's sister organisation in the United States also discovered that the University of Wisconsin-Madison (UW) had been experimenting on cats. PETA challenged the university to reveal photos of the experiments.
"For decades, countless cats have been imprisoned, cut into, and killed in cruel and useless "sound localization" experiments at the University of Wisconsin-Madison .
"When PETA learned that UW experimenters took photographs to document this abuse, we demanded that the school release the photos. Knowing that the public would be outraged if the truth came out, UW fought to keep its cruelty a secret for more than three years, but a successful PETA lawsuit compelled the university to release the images."
PETA has now obtained dozens of disturbing never-before-seen photographs showing the life and death of an orange tabby cat named Double Trouble, who had a variety of experiments carried out on her for three months.
"According to records obtained by PETA, Double Trouble was subjected to invasive surgeries on her ears, skull, and brain. In the first operation, a stainless steel post was screwed to her skull so that her head could be immobilized during experiments," explained PETA.
PETA revealed that in the next surgery, which is depicted in the photographs, experimenters cut into her head and skull and then applied a toxic substance to her inner ears in order to deafen her.
"An antibiotic-resistant bacterial infection resulted from Double Trouble's wound, but experimenters still forced her to endure almost two months of this misery. One of the last entries in Double Trouble's records states that she "appeared Â… depressed," said PETA.
In the end, experimenters noted that she was too ill to continue and that the device they had implanted did not work, so the cat was killed and decapitated so that her brain could be dissected.
A spokesman from the University College London told the Daily Mail that the experiments mentioned in the article were carried out in 1992 and 1998 and that the research highlighted in this story ended in 2010.
A representative from Bristol University said that they could state categorically that the type of research highlighted has not been carried out at the University for at least seven years.
A spokesman from the University of Cambridge said: "The research to which BUAV refers involved scientists from a number of UK institutions, including researchers from University of Cambridge, who analysed tissue samples.
"This research was part of the development of a potential new treatment for amblyopia (lazy eye), a common disorder of vision which affects one in 50 children.
"As it would be unethical to carry out such research using humans, initial studies were carried out using mice and rats; in order to further understand whether the treatment was effective, it was then necessary to carry out further work in a higher order animal – in this case a small number of cats."
PETA is calling on the public to contact these universities and request that they stop these tests.