 By 1747 he had become surgeon of in the Channel Fleet, and conducted his experiment on scurvy while that ship was patrolling the Bay of Biscay.Just after that patrol he left the Navy, wrote his MD thesis on venereal diseases and earned his degree from the University of Edinburgh Medical School, and was granted a licence to practice in Edinburgh.Scurvy is a disease now known to be caused by a vitamin C deficiency, but in Lind's day, the concept of vitamins was unknown.