The Call of The Wild by Jack London Chapter 2 Page 20

Miller’s riding-whip; but the completeness of his decivilization was now evidenced by his ability to flee from the defence of a moral consideration and so save his hide. He did not steal for joy of it, but because of the clamor of his stomach. He did not rob openly, but stole secretly and cunningly, out of respect for club and fang. In short, the things he did were done because it was easier to do them than not to do them.

His development (or retrogression) was rapid. His muscles became hard as iron, and he grew callous to all ordinary pain. He achieved an internal as well as external economy. He could eat anything, no matter how loathsome or indigestible; and, once eaten, the juices of his stomach extracted the last least particle of nutriment; and his blood carried it to the farthest reaches of his body,