He was schooled locally and then studied medicine at the University of Cape Town and Groote Schuur Hospital, where he undertook house-physician and house-surgeon positions.
After six months as a medical registrar in the cardiothoracic department of Wentworth Hospital in Durban he moved to London where he attended the Royal College of Surgeons and obtained his primary fellowship.
[citation needed] Segal then moved to the MRC Clinical Research Centre as registrar in Gastroenterology, during which time he studied Biochemistry at evening classes at Chelsea College of Science and Technology.
He showed that the mechanism by which microbes are killed within the phagocytic vacuole of neutrophils is not through the toxic actions of oxygen free radicals or through the generation of HOCl by myeloperoxidase.
The oxidase elevates the pH within the phagocytic vacuole and drives potassium into this compartment to compensate for the charge generated across the membrane by the passage of electrons.