Keilin became research assistant to
George Nuttall, first
Quick Professor of Biology at the
University of Cambridge, in 1915, and spent the rest of his career there, succeeding Nuttall as Quick Professor and director of the
Molteno Institute in 1931. He retired in 1962. He made extensive contributions to
entomology and
parasitology during his career. He published thirty-nine papers between 1914 and 1923 on the reproduction of lice, the life-cycle of the horse bot-fly, the respiratory adaptations in fly larvae, and other subjects. He is most known for his research and rediscovery of
cytochrome in the 1920s (he invented the name). It had been discovered by C. A. MacMunn in 1884, but that discovery had been forgotten or misunderstood. ==Awards and honours==