George Arnaud Casalis was the son of Eugene Arnaud Casalis (MD Paris, 1862). He was born and practiced medicine in Basutoland (now Lesotho) until about 1893. George was educated in Paris, and subsequently qualified as Bachelor of Medicine (MB) and Master of Surgery (CM) at the University of Edinburgh in 1887. He then returned to France to complete his studies at the University of Paris, whereafter he did some specialist work in gynaecology. Back in southern Africa the University of the Cape of Good Hope admitted him to the degree Bachelor of Medicine in 1893, on the basis of his corresponding qualification from the University of Edinburgh. For the next four years he served as medical officer to the Basutoland Civil Service.
In 1897 Casalis was practising in Port Elizabeth, where he founded a private nursing home, and had become a member of the South African Medical Association. In 1895 he contributed two papers to the South African Medical Journal, one on "Differential diagnosis between small-pox and varicella", the other on "The high plains of the Free State and Transvaal as a health resort for phthisical patients". He returned to the latter topic in an article on the climate of Lesotho in a book by W.C. Scholtz* et al, The South African climate; including climatology and balneology and discussing ... the country as a health resort (1897).
During the Anglo-Boer War (1899-1902) Casalis was attached to the military hospital in Port Elizabeth and later served as a surgeon-captain. He left South Africa in the hospital ship Bavaria, remained in Paris for almost a year for special studies, and returned to Cape Town after the end of the war in the hospital ship Nubia. Starting a practice in Cape Town, he specialised in women's diseases and abdominal surgery, and opened a private hospital at Claremont.
In 1906 Casalis published his only book, The treatment of uterine retro-deviations, in Cape Town. From 1903 onwards he regularly contributed articles to the South African Medical Record, a journal founded (and edited for 21 years) as a private venture by Dr. W. Darley-Hartley*. These contributions, relating to his areas of specialisation, included: "Drainage after abdominal operations" and "Posterior colpotomy in pelvic suppurations" (1903-4, Vol. 1); "Hystero-myectomy for adherent fibroma" (1904, Vol. 2); "Etiology and pathology of uterine prolapse" (1907, Vol. 5); "Cancer of the uterus" (1908, Vol. 6); "Anatomy and physiology of supports of pelvic viscera" (1909, Vol. 7); and "Notes on a short visit to the Johannesburg Hospital", "Some factors which go to make or mar the success of surgical operations", and "The incidence of cancer in South Africa" (1910, Vol. 8). The last of these was a paper he read at the South African Medical Congress in 1910 and was published also in the Transvaal Medical Journal (1910/1, Vol. 6). During 1907-1912 he also published six papers in BJoG: An International Journal of Obstetrics and Gynaecology.
In 1908 Casalis was practising in Adderley Street, Cape Town. By 1910, now practising in Darling Street, he had become a member of the South African Association for the Advancement of Science.