14. Walt Whitman is the globe itself,—all seas, lands, forests, climates, storms, snows, sunshines, rains, of universal earth.
15. A few northern warblers were chirping in the evergreens along the edge of the summit, between the inn and the Point,—black-polls and bay-breasts, with black-throated greens and Carolina wrens; and near there I saw with pleasure my first Tennessee phoebes.
16. The patient has the symptoms resulting from dilatation,—dyspnea and serous effusion.
Without knowing the meaning of the three technical terms in the above sentence, the reader is informed by the comma and dash that “the symptoms” are “dyspnea and serous effusion.”
17. Her economies were frantic child’s play,—methodless, inexperienced, fitful; and they were apt to be followed by remorse.
In this sentence “child’s play” is not sufficiently specific to define “economies”; and therefore the characteristics of “child’s play” are added in the form of a group of adjectives looking back to “economies” and descriptive of child’s play.
18. A young man or a young woman may go, unaided and unfriended, to a large city,—may go with nothing and to nothing,—and yet build up a beautiful and successful life.
In this example the comma is required because it would be required after “city” if the dash group (may go with nothing and to nothing) were omitted. The dashes set off the group, and thus connect what follows the second dash with what precedes the first one.
19. We made a brave effort to smoke the rats out with the vilest imaginable compound of vapors,—brimstone, burnt leather, and arsenic,—and spent a cold night in a deck-bivouac to give the experiment fair play.