The name John Cleland is known to many through Cleland Wildlife Park at Mt Lofty and the J.B. Cleland Kindergarten at St Georges. As a pathologist and naturalist Cleland made an outstanding contribution to knowledge and he was an ardent conservationist.
Cleland was an authoritative botanist. He presented a collection of 30 000 plants, which included 50 new species, to the South Australian Herbarium. He also wrote the first definitive work on the larger fungi of South Australia. As an ornithologist he amassed a large collection of valuable data and bird skins, the latter now housed at the South Australian Museum and the American Museum of Natural History, New York.
As a microbiologist Cleland identified Murray River encephalitis and deter-mined that dengue fever is transmitted by mosquitoes. He also researched and published papers on the harmful effects to humans of plants and animals and, in the field of anthropology, he documented the diseases of Australian Aborigines. Cleland also performed more than 7000 human autopsies, each meticulously documented and the results analysed and published.