Angus was educated at High School, Invercargill, graduating in arts (B.A., B.Sc.) at Otago, New Zealand, and in medicine at Edinburgh University (M.B., Ch.B., F.R.C.S.) entering in 1895 to 1901. After graduating, he devoted himself to ophthalmology and studied at the Moorfields Eye Hospital, where he became a chief clinical assistant, and at Freiburg (where he learnt the German language and became an accomplished French and German Scholar) and Vienna. Angus had previously served in the South African Campaign, in the Edinburgh Hospital, and gained the rank of Captain in 1911. He then returned to Edinburgh and worked as house-surgeon in the Eye Department of the Royal Infirmary, under Professor Berry. He then went abroad and studied Ophthalmology in Vienna, and subsequently in Freiburg, under Professor Axenfeldt. Whilst there he began to learn the language, and began writing articles on his investigations to the German medical papers. From 1905, he became Chief Clinical Assistant at the London Ophthalmic Hospital; Clinical Assistant in the ophthalmic department of Charing Cross Hospital; and Ophthalmic Surgeon at the King Edward VII Hospital, Windsor. He was in practice in Harley Street when war was declared. Angus had been the Medical Officer attached to the London Scottish for over three years, and on the outbreak of war, and at few hours notice left his practice and went into camp with them. Whilst in France, before the regiment was ordered to the front, he did a great deal of surgical work, treating as many as six compound fractures of the thigh in one afternoon. He also provided operating work, when with 100 of the London Scottish acting as stretcher-bearers, he handled trainloads of wounded from the front lines of the Marne and Oise, in a railway goods-shed with few appliances, whilst being forced to kneel on the floor all the time he worked. On the night he was killed at Messines, around 2 a.m., he was already wounded and bleeding freely, but continued his work, calmly bandaging wounded men in the face of the German advance. A despatch rider stated “Dr McNab was actually bayoneted in front of their (the regiment’s) eyes whilst bending down attending to two wounded men. It was bright moonlight, and he had a white badge and Red Cross on his arm and even a blue tunic on, so as to be absolutely unmistakeable, and was of course without arms of any sort.” The two wounded men were also bayoneted. When the officers of the Scottish saw what was described as “the foul deed” they drove back the Germans, giving orders that no prisoners should be taken. Angus was the son of Alexander Macnab; the brother of the Hon. Robert MacNab, Minister of Agriculture in New Zealand; and the husband of Evelyn Macnab - they had two children.