“These were his only pleasures—to eat, to smoke, to sleep, and to play upon his concertina.” 

McTeague is a Naturalist novel in that it examines humans from a scientific standpoint. Naturalist novels often depict their subjects as driven by animal-like internal forces. In this opening passage McTeague is described in his usual Sunday routine. He, like the other characters, is a creature of habit. Just as his Sundays involve watching the scene outside his window on Polk Street, the people of Polk Street follow the same rituals so that “[d]ay after day, McTeague saw the same panorama unroll itself” (9). Later in the novel, after McTeague is forced to stop practicing dentistry, he and Trina fall into a new routine, adjusting to each downward turn in the spiral. Norris’s depiction of people blindly following the same routines not only likens them to animals driven by instinct but also suggests a certain determinism, since behaviors and events cannot be avoided.

“Every other Sunday he became an irresponsible animal, a beast, a brute, crazy with alcohol.” 

This passage describes McTeague’s father. McTeague avoids whiskey, recognizing that it does “not agree with him” (293). However, as time goes on and his quality of life deteriorates, he begins to drink whiskey with his friends. As it did with his father, the whiskey rouses “the brute in the man” and goads “it to evil” (306). Usually docile and slow, McTeague becomes “vicious,” “active,” and “alert” (305); he becomes “intractable” and “mean,” and he takes “a certain pleasure in […] abusing and hurting” Trina (305).