Thomas Lewis's electrocardiograph symbolises the changes medicine underwent in the twentieth century, as machines were increasingly introduced into hospital practice. Electrocardiographs were devices for producing 'traces' - visual records of the heart's electrical activity - and were perhaps the most sophisticated medical machines available before the Second World War. But, perhaps this model's major innovation was the addition of wheels so that it could be wheeled into hospital wards.

These instruments were an essential ingredient of cardiology, the medical speciality which Lewis helped to establish. Doctors such as Lewis argued that advanced laboratory techniques should be transferred to the treatment of patients. Others opposed this mechanisation on the grounds that it devalued hard-won skills and, by creating specialisms based on technical equipment, would make it impossible to consider the patient as a whole person.