13. Upon the appearance before the prescribed enrolling officer of any person desirous of being enrolled, the enrolling officer shall read and explain to him, or cause to be read and explained to him in his presence, the conditions of the service for which he is to be enrolled; and shall put to him the questions set forth in the prescribed form of enrolment, and shall, after having cautioned him that if he makes a false answer to any such question he will be liable to punishment under this Act, record or cause to be recorded his answer to each such question.