Phyllis Margaret Tookey Kerridge

In 1925, supported by DSIR and MRC funding, Kerridge published a paper on her invention of a glass electrode for analysing biochemical samples such as blood.[4] For her biochemical PhD research, Kerridge had required a tool small enough to fit into narrow layers in living tissue, but the design of existing pH electrodes was unsuitable because they provided only very small signals. Kerridge overcame this problem by inventing the miniature pH electrode, with a heat-treated platinum component that gave a much larger signal than the older equipment, enabling accurate measurement even in low fluid volumes.[3] Kerridge noted challenges in developing this equipment, including the high resistance of glass, danger of breakage to the delicate apparatus, and risk of short-circuit.[5]

After qualifying in medicine in the early 1930s, Kerridge was recommended by Dr Edward Poulton to scientific instrument maker Robert W. Paul, who sought someone to conduct rigorous physiological tests on a respirator called the "pulsator" created by William Henry Bragg.[6] Kerridge's tests provided extensive physiological measurements that improved the efficiency of the device, and she also suggested improvements to the design that reduced its complexity and bulk.[6] Mr S. Crosby Halahan, Bragg's neighbour and the inspiration for his respirator, was kept alive via artificial respiration for two years after becoming completely paralysed – Kerridge adapted the design to make it more comfortable for him.[7][8]

In addition to doing much to improve the design of the respirator, Kerridge also played an active role in publicising it. She had photographs taken of her laboratory assistant wearing the device, advised Bragg and Paul to publish their introduction in the Proceedings of the Royal Society of Medicine, and wrote about the features of the case for The Lancet in order that it would reach the attention of General practitioners.[6][9]

Later in the 1930s, Kerridge worked at the Royal Ear Hospital and developed audiometric standards for hearing tests.[6] Kerridge also played a significant role in establishing hearing aid clinics for the deaf.[10] Her keen interest in music inspired her sympathy for those with hearing loss.[2][10] This work particularly focussed on the incidence of deafness in children, and she encouraged her students to accompany her on visits to slums to explore potential factors in the etiology of deafness in school-children.[2] In 1936, the Medical Research Council funded her to test the hearing of schoolchildren across London.[11] Her data was garnered from experiments in the ‘silence room’, a soundproof room of some 3,500 cubic feet in the basement of University College Hospital on Huntley Street in London. This was the first site in Great Britain to have a permanent Western Electric Audiometer that used pure-tone testing rather than speech recording.[1]

Kerridge's expertise in hearing aid technology was used by the British Post Office in its attempts to improve sound quality over telephone lines. The Post Office engineers were initially concerned with Kerridge’s discussion of bone conduction and quoted her extensively in their exploration of improvements to amplified telephony reports.[12] However, she collaborated with the Post Office more extensively when she tested the hearing of telephonists using her audiometer, and in 1937 she installed Post Office amplified telephones designed for people with hearing loss into her clinic.[13] The results of her clinical tests provided data that the Post Office used to improve its amplified telephone service, and the phonetic tests that Kerridge had created with Dennis Butler Fry were later used in the Post Office's design of the Medresco - the first NHS hearing aid.[14]

At the outbreak of the war, Kerridge was working at University College Hospital. She was seconded from there to serve the Emergency Medical Service at St Margaret's Hospital, Epping. There, Kerridge and her colleagues created an improvised laboratory for work in pathology and blood transfusions.[2]

In 1940, Kerridge died aged 38.