Axel Munthe, A Swedish physician living in Paris in the 1880s records in his memoirs some of the scenes and events of medical practice at that time. He tell how there were lots of foreign doctors were practising in Paris and considerable jealousy of the lucrative monopoly in wealthy foreign clientèle. Eventually there was agitation in the press amid hints that many of of these foreigners didn't have qualification from recognised trainings.

'It resulted in an order by the Préfet de Police that all foreign doctors were to present their diplomas for verication before the end of the month. I with my diploma as M.D. of the faculty of Paris was of course all right, I nearly forgot all about it and turned up the very last day at the Commissariat of my quartier.

The Commissaire, who knew me slightly, asked me if I knew a Doctor X., who lived in the same avenue as I did. I answered that all I knew about him was that he must have a very large practice, I had often heard his name mentioned, and I had often admired his elegant carriage waiting outside his house. The Commissaire said I would not have to admire it for long, he was on their black list, he had not presented himself with his diploma because he had none to present, he was a quack, he was going to be pincé * at last. He was said to be making two hundred thousand francs a year, more than many of the leading celebrities in Paris. I said there was no reason why a quack might not be a good doctor, a diploma meant little to his patients as long as he was able to help them.

I heard the end of the story a couple of weeks later from the Commissaire himself. Doctor X. had presented himself at the very last moment with a request for a private interview with the Commissaire. Presenting his diploma as M.D. of a well-known German university, he implored the Commissaire to keep his secret, he said he owed his enormous practice to the circumstance that he was considered by everybody to be a quack. I told the Comissionaire this man would soon become a millionaire if he knew his medicine half as well as he knew his psychology.

Reference
Munthe, Axel (1929) The Story of San Michel John Murray p194
* pincé =to be found out