Conscience is instinct bred in the house, Feeling and Thinking propagate the sin By an unnatural breeding in and in.
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“I have seen some whose consciences, owing undoubtedly to former indulgence, had grown to be as irritable as spoilt children, and at length gave them no peace. They did not know when to swallow their cud, and their lives of course yielded no milk. Conscience is instinct bred in the house, Feeling and Thinking propagate the sin By an unnatural breeding in and in. I say, Turn it out doors, Into the moors. I love a life whose plot is simple, And does not thicken with every pimple, A soul so sound no sickly conscience binds it, That makes the universe no worse than ’t finds it.” source