Sentence:  When even the silence and seclusion of this retreat failed to bring slumber, he sometimes called in a professional mesmerizer to put him into a hypnotic sleep, from which Sawyer knew how to arouse him at a fixed time. This habit, as well as the existence of the underground chamber, were secrets known only to Sawyer and the hypnotist who rendered his services. On the night of May 30, 1887, West sent for the latter, and was <WSD>put to sleep</WSD> as usual. 
Meaning of the word marked with <WSD> tags:  To cause (someone) to sleep.