Crookshank studied at
King's College London and qualified for medicine in 1881. He served briefly as an assistant to
Joseph Lister, a physician noted for his work promoting
antiseptics and
sterile surgery. In 1882, Crookshank served as a doctor with the British armed forces sent to
Egypt as a result of the
Urabi Revolt; he was decorated for his service at the
Battle of Tel el-Kebir. On return from Egypt, Crookshank toured Europe in 1884 for further medical training. In Berlin, he visited the laboratory of
Robert Koch and learned methods of isolating bacterial strains to investigate
infectious diseases. When he returned to London, Crookshank wrote a textbook,
An Introduction to Practical Bacteriology Based on the Methods of Koch, which was published in 1886. Subsequent editions were published under differing titles in 1887, 1890 and 1896, and a French translation by H. Bergeaud was published in Paris as soon as 1886. In 1885, Crookshank founded one of the world's first bacteriological laboratories for human and
veterinary pathology in London. Crookshank was also interested in the use of photography to study bacteria and published
Photography of Bacteria in 1887, the first text in English devoted solely to the photography of bacteria. In the introduction to this book he wrote that the photographs were "intended to convince scoffers of the essential truth of the new Science, that specific, often morphologically distinct, microorganisms were the cause of particular infectious diseases". During this time he became interested in the study of infectious diseases in animals and in 1886 was awarded the chair of Comparative Pathology and Bacteriology at
King's College London. In his new role he was asked to investigate an outbreak of
cowpox in
Lechlade,
Gloucestershire. His investigations led him to reconsider the use of
cowpox-derived
vaccines to immunize against
smallpox, a treatment developed by
Edward Jenner nearly a hundred years earlier. His conclusion was that such
vaccines were ineffective in preventing smallpox because the two diseases (cowpox and smallpox) were "totally distinct". Instead of a cowpox-derived vaccine, he advocated the use of a more dangerous vaccination using
attenuated smallpox. In 1889, he published a two-volume treatise on the subject,
A History and Pathology of Vaccination. Vaccination policies were a divisive topic at the time and in the ensuing controversy that resulted from his publication, Crookshank quit his chair at King's College London in 1891. He continued to speak out on health matters, but never worked in a laboratory again. He subsequently, however, focused on the encouragement of agricultural and veterinary science, serving as a governor of the
Royal Veterinary College until his death. In 1894, Crookshank was appointed
Justice of the Peace for
Sussex, and in 1906 stood unsuccessfully as
East Grinstead's parliamentary candidate as a
Unionist and
tariff reformer. In later life, he travelled extensively in the
Dominions, becoming a skilled
big-game hunter and deputy chairman of two Scottish-Australian corporations. == Publications ==