Born at Weybridge on 15 May 1862, third son of Arthur Cobbett, provision merchant, and his wife Betsey Holt, and their ninth and youngest child. He was educated at Lancing and Trinity College, Cambridge, where he took third-class honours in the Natural Sciences tripos part I, 1884, and came under the influence of Sir George Murray Humphry, FRCS, professor of surgery and formerly professor of anatomy in the university. At St Thomas's Hospital, where he took his clinical training, he served as house surgeon to Sir William MacCormac, FRCS, but after taking the Fellowship in 1891 his interest turned to pathology. He went back to Cambridge in 1893 as university demonstrator under Charles Roy, FRS (1854-97), the first professor of pathology, and was elected John Lucas Walker student of pathology, 1894-97. Cobbett at this time was chiefly occupied with the development of antitoxin, with special reference to diphtheria. He took the MD in 1899 by thesis "On the nature of the action of antitoxin". During the Cambridge and Colchester epidemics of 1900-01 he made the first large-scale investigations into the bacteriology of diphtheria, publishing his results in the first volume of the *Journal of Hygiene*, Cambridge University Press, 1901, and with G H F Nuttall and T H P Strangeways he discussed the cultural characters found in 950 examinations of the diphtheria bacillus. Cobbett next turned his attention to tuberculosis. At the British Congress on Tuberculosis in 1901 Robert Koch announced that he had proved that human and bovine tuberculosis were distinct entities, the human strain not being transmissible to cattle. Lister, who was in the chair, at once pointed out that the converse did not follow, and that it still remained to be proved whether or not bovine tuberculosis was communicable to man. The Royal Commission on Tuberculosis, appointed in 1902, set up a positive programme of research, and Cobbett was chosen as pathological investigator with charge of their experimental farm at Stansted. The very valuable results obtained by Cobbett's team, all the other members of which he survived, were published in a series *Reports* from 1907 to 1913; the Commission also published a *Report on tuberculin tests* by Cobbett and Stanley Griffith in 1913. Cobbett published his personal survey of this work as *The causes of tuberculosis, together, with some account of the prevalence and distribution of the disease*, Cambridge University Press, 1917. The book missed its merited success by appearing in the darkest year of the first world war; it has however achieved the rank of a classic in its own field. He also published an original study of Racial immunisation in tuberculosis. Cobbett was appointed to the professorship of pathology at Leeds in 1907, but held the chair for only a year. He went back to Cambridge, where from 1908 until 1929 he was university lecturer in pathology and proved himself a keen teacher with a kindly interest in his students; he was always ready to discuss with enthusiasm every subject in which he was interested. He worked with G S Graham Smith on the pathology of grouse disease, and their results were included in the *Report of the Commission on grouse disease* in 1911. He served as vice-president of the section of pathology and bacteriology at the British Medical Association annual meeting 1920. After his retirement he continued to work in the university pathology department and to lecture for part 2 of the Natural Sciences tripos. Cobbett died, after one day's illness, at his house Inchmahone, Adam Road, Cambridge, on 9 March 1947, aged 85; he was unmarried. He bequeathed £1,000 each to Addenbrooke's hospital and the department of pathology at Cambridge, and to the latter his medical books. His principal publications have been mentioned in the course of the memoir above.