Hillman caused controversy in biological fields with his insistence that structures seen in cells under the electron microscope were little more than artefacts. He maintained that up to 90 percent of the brain is made up of "a fine, granular material that is virtually liquid" and that the brain only has two cell types, as opposed to four.
Mainstream scientists maintained that as fixation techniques have been compared with other analysis techniques, and that there is no explanation for why all the different techniques should produce identical artifacts.
Hillman's main field was neurobiology and resuscitation, in which his work was largely uncontroversial.
Hillman was Reader in Physiology at the University of Surrey from 1965 until 1989, when he took early retirement after being threatened with loss of tenure. He wrote in 1996 that "I believe that I am the only tenured academic in Britain who has lost his tenure because of his or her scientific views."
- What price intellectual honesty?” asks a neurobiologist, published in Brian Martin (editor), Confronting the Experts (Albany, NY: State University of New York Press, 1996), ISBN 9780791429143, pp. 99-130 (includes a bibliography of his works to 1996)
- Hillman, Harold (1986). The Cellular Structure of the Mammalian Nervous System: A re-examination, and some consequences for neurobiology. Springer Science & Business Media. ISBN 978-94-009-4922-5.
- Richard Stevenson, Good Scientists, Bad Science? Clinging To A 'Dubious' Position Can Destroy A Career, The Scientist, July 25, 1988
- Hillman, 1996, p.71: "The greatest proportion of the central nervous system is a ground substance consisting of a fine granular material with ‘naked nuclei.’"
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- Hillman, 1996, p.73
- Hiliman, H. (1993). "The possible pain experienced during execution by different methods". Perception. 22 (6): 745–821. doi:10.1068/p220745.
- Hillman, Dr.: Obituary, Surrey Herald