He is sometimes known as the father of British microbiology but most of his work in microbiology and bacteriology was overshadowed during his life by his use of and outspoken support for animal vivisection in physiological and medical experiments. After graduating in the local school, he went to study medicine at Vienna and obtained an Doctor of Medicine in 1869. The hosts, John Burdon Sanderson and John Simon were impressed by his knowledge and they invited Klein to work in London in 1871.
Klein moved to the Brown Animal Sanatory Institution and in 1873, became a professor of comparative pathology.
He also worked at Saint Bartholomew"s Hospital where he was made a joint professor of general anatomy and physiology. His work on animal physiology was published in Handbook for the Physiological Laboratory in 1873, along with Burdon Sanderson, Thomas Lauder Brunton and Michael Foster and they made use of experimental methods on living animals, something that were considered acceptable in the Vienna Medical School.
The anti-vivisection movement protested the methods described in their textbook and in 1875, after he was elected Fellow of the Royal Society, the Royal Commission on Vivisection for Scientific Purposes held its hearings and although Foster, Brunton and Burdon Sanderson were careful in responding to the queries, Klein responded without any apparent remorse. Klein tried to provide a revised text of his responses but the Royal Commission rejected this.
Klein was made into a monster by the media and he became the main target of the anti-vivisectionists and the case led to the establishment of the Cruelty to Animals Acting 1876.
The media coverage during the anti-vivisection case made Klein widely infamous. Several novels of the period were inspired by the case including Paul Faber, Surgeon (1878) by George MacDonald. The Professor"s Wife (1881) by Leonard Graham and Heart and Science (1883) by Wilkie Collins.
These novels included a scientist as a key character modelled after Klein and juxtaposed with a range of negative traits and ethnic stereotypes.
Klein"s training in Europe however allowed him to access the microbiological techniques developed by Louis Pasteur and Robert Koch and he wrote the first major English work in bacteriology in 1884. In the same year, Klein and Heneage Gibbes were sent as part of the British cholera commission to Calcutta in India to verify the findings of Koch which had caused a bit of embarrassment to the British Indian medical community.
Klein was able to find the comma-shaped Vibrio cholerae bacteria in the water supply where Koch had found them as well as in the stools of infected patients. He however did not fully accept the idea that the same bacteria caused the disease.
In 1885, he studied the outbreak of a disease of cows which was termed as scarlet fever and isolated four species of bacteria during the research which included Streptococcus pyogenes, the causal agent.
Klein also worked on bacteria in food and helped in establishing methods for food processing and preservation. Of the 264 scientiﬁc publications in his career nearly 200 were in microbiology. Ronald Ross was one of Klein"s students.
Klein"s had married Sophia Mawley in 1877 and she died in 1919.
He died at his home in Hove on February 9th, 1925.