Arrowsmith begins with a third-person account of Martin Arrowsmith's great-grandmother, who's helping her family cross the American countryside. Only a page later, though, the third-person narrator plunges us right into the middle of Martin Arrowsmith's young life:
Cross-legged in the examining-chair in Doc Vickerson's office, a boy was reading 'Gray's Anatomy.' (1.2.1)
Notice here that the narrator (and Sinclair Lewis) is really giving us an outside shot of Martin—even before telling us his name. As the novel unfolds, the narrator sometimes leaves Martin entirely and follows the trials of Max Gottlieb. Or, in a weird twist, the narrator even focuses on the character of the plague:
From Yunnan in China, from the clattering bright bazaars, crept something invisible in the sun and vigilant by dark, creeping, sinister, ceaseless. (31.1.1)
This constant hopping around—paying attention to lesser characters like grandma, Gottlieb and the freaking plague—is what gives the book the unmistakable stamp of Third-Person Omniscience.