Since the number of physicians per population might not increase beyond the break-even point due to the fear of operating at a loss, there might be a minimal population size for medical practice. In this paper, I determined the sizes of municipalities in which at least one physician with each medical specialty worked.
Internists worked in more than half of the villages of less than 1,000 people. For municipalities in more than 50% of which physicians with other medical specialties worked, the minimal population sizes were as follows：pediatricians, surgeons, orthopedists and ophthalmologists, 10,000；cardiologists, gastroenterologists, dermatologists, psychiatrists, urologists, neurosurgeons, otolaryngologists, obstetricians/gynecologists, 30,000；neurologists, radiologists, digestive surgeons and anesthesiologists, 50,000；respiratory physicians, diabetologists and physiatrists, 70,000；nephrologists, psychotherapists, respiratory surgeons, cardiovascular surgeons, plastic surgeons and gynecologists, 100,000；hematologists, rheumatologists, breast surgeons and colorectal surgeons, 200,000；cosmetic surgeons, pediatric surgeons and obstetricians, 300,000；allergists, 500,000.
In the municipalities beyond these minimal population sizes, physicians with each specialty per population were roughly constant.

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