In case of the absence, disability or disqualification of any municipal judge in any court affected by this act, or in any other court organized under any other municipal court act of this state, in which the judge is paid a salary in lieu of fees and is required to be an attorney at law, and having the jurisdiction of a justice of the peace, in a city, or having jurisdiction to hear and determine violations of the ordinances of said city, or both, any other municipal judge of any city in this state, under this act or any other municipal court act of this state, who is paid a salary in lieu of fees and who is an attorney at law, shall be qualified to act in the place of and for such municipal judge in the performance of any of the duties imposed upon him by law in all matters civil and criminal and in all matters pertaining to violations of the ordinances of such city, under the conditions and in the manner hereinafter set forth; and such substitute judge shall, when called upon in the manner and under the conditions set forth, so act: Provided, That in case any municipal judge of any of the foregoing courts shall be unable to hear and determine cases pending in his court without unreasonable delay, because of the volume of cases awaiting determination, he may request and obtain the assistance of any other municipal judge of any city in this state, as above defined, to assist him in the trial of cases and the performance of the duties imposed upon him by law in all matters criminal and civil and in all matters pertaining to violations of the ordinances of such city, under the conditions and in the manner hereinafter set forth.