"Then only shout in the right places, and you'll do." No doubt this implied that even in the matter of shouting some science is involved.

And there may be men who cannot shout at all, let the places be right or wrong.

Still the stage can find room and subsistence of a sort for all, even for mutes.

But carry a banner, walk in a procession, or form one of a crowd, and you may still call yourself actor, though not an actor of a high class, certainly.

The histrionic calling is a ladder of many rungs.