Whenever in a contested case the officials of the agency who are to render the final decision have not heard and examined all of the evidence, the decision, if adverse to a party to the proceeding other than the agency itself, shall not be made until a proposal for decision containing a statement of reasons and including determination of each issue of fact or law necessary to the proposed decision has been served upon the parties, and an opportunity has been afforded to each party adversely affected to file exceptions and present argument to the officials who are to render the decision, who shall personally consider the whole record or such portions thereof as may be cited by the parties.