An Act amending the act of March 18, 1875 (P. L. 28, No. 31), entitled "An act to authorize the judges of the several courts throughout the Commonwealth to fix the number of the regular terms of said several courts and the times for holding the same, the time for summoning the grand jury and for the returns of constable, alderman and justices of the peace to the same," providing for investigative grand juries, their operation and the rights of those called for such duty.