How we cite our quotes: (Chapter.Section.Paragraph)
Quote #1
Burned in his mind was an image of beauty and tenderness, a sweet and holy girl, precious beyond thinking, clean and loving, and that image was Cathy to her husband, and nothing Cathy did or said could warp Adam's Cathy. (13.2.4)
Looks like Adam has got a bad case of love-blindness. In this case, his innocence is in the form of the fact that the real Cathy hasn't been revealed to him yet. If Adam were a little more perceptive, he might see the little hints that Cathy isn't all sweetness and rainbows, but the fact is that Adam doesn't want to see the bad side of Cathy. So his innocence is a bit of his own doing too.
Quote #2
Samuel said satirically, "It's my duty to take this thing of yours and kick it in the face, then raise it up and spread slime on it thick enough to blot out its dangerous light." His voice grew strong with vehemence. "I should hold it up to you much-covered and show you its dirt and danger. I should warn you to look closer until you can see how ugly it really is. I should ask you to think of inconstancy and give you examples. I should give you Othello's handkerchief. Oh, I should. And I should straighten out your tangled thoughts, show you that the impulse is gray as lead and rotten as a dead cow in wet weather." (15.3.75)
What the heck is this thing Samuel is talking about? From the looks of it, it sounds like he's referring to Adam's blind infatuation with Cathy. He is being really prophetic here, which make sense because his biblical namesake Samuel was a prophet. And what is he prophesizing exactly? That Adam has some serious heartbreak on the horizon. As a good friend, he should break through Adam's innocence and show him all of the reasons why Cathy isn't as great as Adam thinks she is. Ironically though, being a good friend would mean destroying Adam's happiness, so Samuel lets Adam keep his innocence—for the time being.
Quote #3
"Adam, do you want the medicine?"
"Yes, I don't know what it is but give it to me."
"Adam, Cathy is in Salinas. She owns a whorehouse, the most vicious and depraved in this whole end of the country […] Now, there's your medicine. Let's see what it does to you."
"You're a liar!" Adam said.
"No, Adam. Many things I am, but a liar I am not."
Adam whirled on Lee. "Is it true?"
"I'm no antidote," said Lee. "Yes. It's true." (24.3.31-37)
Samuel is using the metaphor of medicine for the truth—a truth that will shatter Adam's innocence, and that he may or may not be ready to hear. Later, after Adam runs off into the bushes, Lee comments that Samuel's medicine acts like poison. But remember what Samuel said earlier about how if he were a good friend he would ruin Adam's image of Cathy and save him a world of trouble? Well now he's being a good friend, so to speak. It's medicine in the sense that it draws back the veil that has been covering Adam's world, and now he can move on.