What work is the quote an allusion to? Why did Sinclair employ this allusion?

From the text:

All this while that he was seeking for work, there was a dark shadow hanging over Jurgis; as if a savage beast were lurking somewhere in the pathway of his life, and he knew it, and yet could not help approaching the place. There are all stages of being out of work in Packingtown, and he faced in dread the prospect of reaching the lowest. There is a place that waits for the lowest man—the fertilizer plant!