Section 27. Every such board shall organize annually by the choice of one of its number as chairman. It may make rules and regulations for its own government and for the government of its officers, agents and assistants. It may appoint a physician to the board, who shall hold his office during its pleasure, may choose a clerk, who in a city shall not be a member of the board, and may employ the necessary officers, agents and assistants to execute the health laws and its regulations. It may fix the salary or other compensation of such physician and its clerk and other agents and assistants.