Mich. Comp. Laws § 768.18

Sec. 18. (1) Any judge of a court of record in this state about to try a felony case which is likely to be protracted, may order a jury impaneled of not to exceed 14 members, who shall have the same qualifications and shall be impaneled in the same manner as is, or may be, provided by law for impaneling juries in such courts. All of those jurors shall sit and hear the cause. Should any condition arise during the trial of the cause which in the opinion of the trial court justifies the excusal of any of the jurors so impaneled from further service, he may do so and the trial shall proceed, unless the number of jurors be reduced to less than 12. In the event that more than 12 jurors are left on the jury after the charge of the court, the clerk of the court in the presence of the trial judge shall place the names of all of the jurors on slips, folded so as to conceal the names thereon, in a suitable box provided for that purpose, and shall draw therefrom the names of a sufficient number to reduce the jury to 12 members who shall then proceed to determine the issue presented in the manner provided by law.