Section 10. Each person conducting a demonstration sheep farm shall maintain under the supervision of and in accordance with such rules and regulations as may be prescribed by the commissioner, a flock of not less than twenty sheep and under his direction may from time to time purchase and sell such sheep as may be considered essential to the proper development of the industry in the locality of such farm, the sheep so purchased or sold to be passed upon by the division of animal health as to their condition and freedom from disease.