Read it through once

“But what do you mean by a _change_, Mr. Heathcliff?” I said, alarmed at his manner: though he was neither in danger of losing his senses, nor dying, according to my judgment: he was quite strong and healthy; and, as to his reason, from childhood he had a delight in dwelling on dark things, and entertaining odd fancies. He might have had a monomania on the subject of his departed idol; but on every other point his wits were as sound as mine.