Sentence:  ... abruptly, his head craned into the limited space between Mrs. Silsburn and me. “Driver,” he said peremptorily, and waited for a response. When it came with promptness, his voice became a bit more <WSD>tractile</WSD>, democratic: “How long do you think we'll be tied up here?” 
Meaning of the word marked with <WSD> tags:  Capable of being led.