“ A clerk of the collector is not an officer of the United States within the provisions of this section; and it is only to persons of that rank that the term public officer, as there used, applies. An officer of the United States can only be appointed by the president, by and with the advice and consent of the senate, or by a court of law, or the head of a department. A person in the service of the government who does not derive his position from one of these sources is not an officer of the United States in the sense of the constitution. ”

“ The officers specifically designated in section 3639 are all charged by some act of congress with duties connected with the collection, disbursement or keeping of the public moneys, or to perform other duties as fiscal agents of the government. ”