Obviously, the slaughterhouses in The Jungle are the subjects of Upton Sinclair's journalistic investigation, so they have a literal importance as the whole novel's reason for being. At the same time, Jurgis and his family's introduction to the modernized, mechanized slaughterhouse has an unfortunate symbolic resonance. Filled with pity, Jurgis watches a row of hogs going peacefully down a chute to the killing floor. He does not realize that he and his family, like those doomed pigs, are trooping equally quietly to their own doom. Consider the following description from Chapter 3, when Jurgis and his family first tour Brown's pork processing plant:
It was all so very businesslike that one watched it fascinated. It was pork-making by machinery, pork-making by applied mathematics. And yet somehow the most matter-of-fact person could not help thinking of the hogs; they were so innocent, they came so very trustingly; and they were so very human in their protests – and so perfectly within their rights! They had done nothing to deserve it, and it was adding insult to injury, as the thing was done here. (3.32)
The pigs are "so innocent" and come "so very trustingly" to the slaughter. We can compare their pitiable response to Jurgis's own eager volunteering to join the ranks of the meatpackers. He has absolute faith in the efficiency and value of these factories. He has no idea how much harm they will do to him. What is more, once Jurgis does realize how unjust the factory system is, he, like the hogs, is "perfectly within [his] rights" to protest. He has "done nothing to deserve" his fate. The slaughterhouses of The Jungle are not just convenient targets for Sinclair to expose to the public. They also serve as a larger metaphor for how American business treats its laborers, by luring them in to unsafe working conditions and then consuming their dedication and strength.