Sentence:  To none of these evidences of a fearful tragedy of a long dead day did little Tarzan give but passing heed. His wild jungle life had <WSD>inured</WSD> him to the sight of dead and dying animals, and had he known that he was looking upon the remains of his own father and mother he would have been no more greatly moved. 
Meaning of the word marked with <WSD> tags:  To cause someone to become accustomed to something (usually) unpleasant. (from 16th c.)