The justices of the supreme court and judges of the district courts shall receive for their services such compensation as may be provided by law, which shall not b e diminished during their terms of office, unless by general law applicable to all salaried officers of the state. Such justices or judges shall receive no fees or perquisites nor hold any other office of profit or trust under the authority of the state, or the United States except as may be provided by law, or practice law during their continuance in office.