Proceedings for involuntary hospitalization by judicial procedure may be commenced by filing a written petition with the probate court of the county where he is present or where he is a resident by any interested person or the superintendent of any public or private mental institution in which he may be. The petition shall be served on the person and his attorney and if he has no attorney then on him and a member of his immediate family.

The petition shall be accompanied by a certificate of a designated examiner stating that he has examined the person and is of the opinion that he is mentally ill and should be hospitalized or a written statement by the petitioner that the person has refused to submit to an examination by a designated examiner. The certificate or the written statement shall state the underlying facts upon which the examiner or petitioner, if the person has refused to submit to an examination, bases his conclusions and not merely the conclusions themselves.