In hard times, even the simplest things can be worthy of admiration. "Potatoes, eggs, and sausages" may not sound that exciting, but for someone on the verge of starving, it's "overwhelming." Jacob may sound like he's exaggerating, but during the Depression, encountering such bounty would indeed be "like [seeing] manna from heaven."

The implication here is that any guy who doesn't give in to this sales pitch isn't "a red-blooded American" and doesn't have "manly blood." You can see how this would work on a bunch of guys who are already at the circus to escape their downtrodden lives. In order to prove their masculinity, the customers are asked to pay up and view the "amazing" and "shocking" exhibit.

From the first time we meet him, the younger Jacob is concerned about his lack of knowledge about sex and how it's interfering with his ability to grow up. At the circus, he starts to fill in the gaps.