When any person shall be elected or appointed to the office of constable he shall repair to the clerk’s office of the county and, together with the evidence of his election or appointment, he shall lodge his bond in the form prescribed by law in the penalty of five hundred dollars, with good sureties, not less than two nor more than five, to be approved in writing by the clerk. Upon taking the oaths herein prescribed such person shall be entitled to a certificate from the clerk that he has filed his bond and taken the requisite oaths and shall thenceforth be regarded as a regularly qualified constable. No person not so qualified shall exercise the powers of a constable, except as otherwise expressly provided and except that nothing herein contained shall prevent a presiding judge, a magistrate or a coroner from appointing a constable to act by virtue of such appointment only on a particular occasion, to be specified in writing.