As Barstow went out, Donaldson crossed to the chemist's desk. He fumbled nervously among the bottles until he found the little vial Barstow had pointed out. He had just time to thrust this into his pocket and reseat himself before Barstow returned. At the same moment there was a firm but decidedly feminine knock upon the outer door. The chemist seemed to recognize it, for instead of his usual impatient shout he went to the door and opened it. And yet, when the feeble light revealed his visitor he evinced surprise. "What, you, Miss Arsdale?" [Illustration: "_What, you, Miss Arsdale?_"] "Yes, Professor," she answered, slightly out of breath. "I thought that if I hurried I might possibly find you here. I am all out of my brother's medicine and I did not dare wait until to-morrow." "I 'm glad you did n't," he responded heartily. "If you will sit down a moment I will prepare it." Donaldson glanced up, irritated to think he had not left earlier and so escaped the inevitable introduction. He saw a young woman of perhaps twenty-two or three, and then--the young woman's eyes. They were dark, but not black, a sort of silver black like gun metal. They were, he noted instantly, apparently more mature than the rest of her features, as is sometimes true when the soul grows out of proportion to the years. Her hair was of a reddish brown; brown in the shadows, a golden red as she stood beneath the gas-jet. She was a little below medium height, rather slight, and was dressed in a dark blue pongee suit, the coat of which reached to her ankles. One might expect most anything of her, thought Donaldson, child or woman. It would no more surprise one to see her in tears over a trifle than standing firm in a crisis; bending over a wisp of embroidery, or driving a sixty horse-power automobile. Of one thing Donaldson thought he could be sure; that whatever she did she would do with all her heart. These and many other fugitive thoughts passed through Donaldson's brain during the few minutes he was left here alone with her. What was said he could not remember a minute afterwards; something of the night, something of the brilliant reflections of the gas-light in the varicolored bottles, something of the approaching summer. Her thoughts seemed to be as far removed from this small room as were his own. "Your patient is better?" Barstow inquired, when he returned with the package. Her face lightened instantly. "Yes," she answered, "much better." "Good." He added, "I should n't think it safe for you to be out alone at night. Have n't there been a good many highway robberies recently in your neighborhood?" "You have heard?" "It would be difficult to listen to the newsboys and not hear that. The last one, a week ago, made the fourth, didn't it?" "I don't know. I seldom read the papers. They are too horrible." "I will gladly escort you if--"