They were all physicians. Indeed, there are societies of medical authors in many countries, and physician-writers even have a Wikipedia entry –http://en.wikipedia.org/wiki/Physician_writer).
Claude Bernard is not listed, although in his late teens he wrote his play Rose du Rhone, which was successful enough to provide the money for him to move to Paris from his native Beaujolais: he wanted to woo the world of drama with his new five-act Arthur de Bretagne. Harshly put in his place by the eminent drama critic, Saint Marc Girardin, he was steered towards medical studies. Not that much later, the sheer eloquence of his scientific presentations drew crowds from all corners of the globe to his public lectures at the Collège de France. He was soon invited to write for the illustrious Revue des Deux Mondes. His crowning glory was election to the Académie Française : not so much for his science, but for the literary quality of his copious written output, including his almost biblical reference book, the Introduction to the Study of Experimental Medicine.
The interested can find all this detailed in my novel, A Matter of Doubt http://tinyurl.com/matterofdoubt It also forms the subject of my talk, Claude Bernard extraordinaire – scientifique et littéraire at the Médiathèque of Monaco on May 2nd at 18.00.
The nature of the link between medicine and literary ability is highly complex and is much debated. However, the discipline of Medical Humanities has evolved from the link, with the realization that literacy contributes to the performance and the understanding of physicians – http://medhum.med.nyu.edu/.