The most obvious metaphor in "Seventh Street" is blood, specifically "black reddish blood." This blood represents southern blacks who have been in an immigration movement up to Washington DC in this time period. The white people who already lived in DC are represented by the "white and whitewashed wood of Washington." The narrator seems to describe the whites living in DC negatively, describing the wood as stale and soggy causing wedges to rust. This sogginess may or may not be caused by the blood. The cause is not stated.
The phrase “who set you flowing?” is used repeatedly, as if to say “Why are you here? Who invited you?” Then the blood is described as running down Seventh Street (probably a black neighborhood in this time) into all the neighborhood buildings. This describes blacks as they assimilate into and dominate Seventh Street in all aspects of the community. This is significant because “white and whitewash disappear in blood.” This disappearance could imply “white flight” (the idea that white people leave areas that people of other racial backgrounds begin to take over). Or it could bring up the age old dichotomy of white v. dark representing purity v. impurity. In other words people of other ethnicities (represented through color) corrupt the pure (white) society already in place, removing its purity altogether.
The narrator refers more negatively to the blacks through comments about drinking blood. He implies alcoholism through the statement “Blood suckers of the War would spin in a frenzy of dizziness if they drank your blood. Prohibition would put a stop to it.” The use of “prohibition” specifies alcohol is involved, and the narrator describes some effects of drunkenness in the people who hypothetically drank the black red blood. Then the narrator says, “God would not dare to suck black red blood. A Nigger God! He would duck his head in shame and call for the Judgement Day.” The use of the word “Nigger” implies a low view of blacks, but God’s rejection of blacks implies the inferiority of blacks to whites, even in God’s eyes. The narrator implies not only that God rejects blacks and is ashamed of them, but that He would end the world if he “drank the blood” of black people. I would assume drinking the blood means associating with and accepting black people.