The Island of Doctor Moreau by H. G. Wells

The study of Nature makes a man at last as remorseless as Nature. I have gone on, not heeding anything but the question I was pursuing; [Dr. Moreau responds to his creations being called abominations; ethics doesn't come into it]

“This silly ass of a world,” he said; “what a muddle it all is! I haven't had any life. I wonder when it's going to begin. Sixteen years being bullied by nurses and schoolmasters at their own sweet will; five in London grinding hard at medicine, bad food, shabby lodgings, shabby clothes, shabby vice, a blunder,—I didn't know any better,—and hustled off to this beastly island. Ten years here! What's it all for, Prendick? Are we bubbles blown by a baby?” [Montgomery musing on the meaning of life]

...he got up, and went for the brandy. “Drink!” he said returning, “you logic-chopping, chalky-faced saint of an atheist, drink!” [A drunk Montgomery pressing Prendick]

I may have caught something of the natural wildness of my companions. They say that terror is a disease, and anyhow I can witness that for several years now a restless fear has dwelt in my mind. [Prendick analysing his experience on the island]

The Scarlet Letter by Nathaniel Hawthorn

Here was the iron link of mutual crime, which neither he nor she could break. Like all other ties, it brought along with it its obligations. [Hester Pryne and Arthur Dimmesdale are bound together by their crime]

May God forgive us both. We are not, Hester, the worst sinners in the world. There is one worse than even the polluted priest! That old man's revenge has been blacker than my sin. He has violated, in cold blood, the sanctity of a human heart. Thou and I, Hester, never did so! [Talking about the malevolent Roger Chillingworth who is psychologically torturing the minister]

...the infectious poison of that sin had been thus rapidly diffused throughout his moral system.