A quorum of the grand committee shall consist of a majority of all the members of the senate and a majority of all the members of the house of representatives duly assembled pursuant to an invitation from one of said bodies which has been accepted by the other, and the acceptance of which has been communicated by message to the body in which such invitation originated, and each house shall be attended by its secretaries and clerks. No act or business of any kind shall be done in grand committee other than that which is distinctly specified in the invitation by virtue of which such grand committee is assembled, except to take a recess or to dissolve; provided, that the grand committee may appoint a subcommittee of its own members to count any ballots delivered to it and report the result of such count.