Prohibits corporations and business entities from practicing medicine. The doctrine attempts to prohibit business people and lay people without medical licenses from practicing medicine and prevent doctors from avoiding liability by incorporating. This bars companies from hiring doctors to treat their employees and also bars doctors and health care professionals from incorporating. However, there are many exceptions to the doctrine (statutes enacted removing HMOs from the reach of the doctrine), and doctors are allowed to form Professional Corporations (PCs). The doctrine is outdated and many say that it needs to be reexamined in light of the changes to the health care delivery systems across the country.