Conan Doyle met Dr. Bell in 1877 at the University of Edinburgh Medical School, where he was studying to be a doctor and Bell was one of his professors.  

Bell was thirty-nine years old when Conan Doyle first attended one of his lectures.  He is said to have walked with a jerky kind of a step that communicated great energy.  His nose and chin were angular and his eyes twinkled with shrewdness.  In addition to being a brilliant doctor, Bell was also an amateur poet, a sportsman and a bird-watcher.

By the end of Conan Doyle's second year Bell had selected him to serve as an assistant in his ward.   This gave Conan Doyle the opportunity to view Dr. Bell's remarkable ability to quickly deduce a great deal about a patient.  

Dr. Bell observed the way a person moved.  The walk of a sailor varied vastly from that of a soldier.  If he identified a person as a sailor he would look for  any tattoos that might assist him in knowing where their travels had taken them.   He trained himself to listen for small differences in his patient's accents to help him identify where they were from.  Bell studied the hands of his patients because callouses or other marks could help him determine their occupation.  

So while Conan Doyle went on to write about the brilliant Sherlock Holmes, he played Dr. Watson, at least for awhile, to his professor. 

"In teaching the treatment of disease and accident," Dr. Bell stated, "all careful teachers have first to show the student how to recognize accurately the case.  The recognition depends in great measure on the accurate and rapid appreciation of small points in which the diseased differs from the healthy state.  In fact, the student must be taught to observe.  To interest him in this kind of work we teachers find it useful to show the student how much a trained use of the observation can discover in ordinary matters such as the previous history, nationality and occupation of a patient."