As she spoke, she had quickly detached the little instrument and had placed it on Annie Grayson’s arm.  If it had been a Bertillon camera, or even a finger-print outfit, Annie Grayson would probably have fought like a tigress.  But this thing was a new one.  She had a peculiar spirit of bravado.

“Such terms as kleptomania,” went on Constance, “are often regarded as excuses framed up by the experts to cover up plain ordinary stealing.  But did you wiseacres of crime ever stop to think that perhaps they do actually exist?

“There are many things that distinguish such a woman as I have described to you from a common thief.  There is the insane desire to steal—­merely for stealing’s sake—­a morbid craving.  Of course in a sense it is stealing.  But it is persistent, incorrigible, irrational, motiveless, useless.

“Stop and think about it a moment,” she concluded, lowering her voice and taking advantage of the very novelty of the situation she had created.  “Such diseases are the product of civilization, of sensationalism.  Naturally enough, then, woman, with her delicately balanced nervous organization, is the first and chief offender—­if you insist on calling such a person an offender under your antiquated methods of dealing with such cases.”

She had paused.

“What did you say you called this thing?” asked Drummond as he tapped the arrangement on Annie Grayson’s arm.

He was evidently not much impressed by it, yet somehow instinctively regarded it with somewhat of the feelings of an elephant toward a mouse.

“That?” answered Constance, taking it off Annie Grayson’s wrist before she could do anything with it.  “Why, I don’t know that I said anything about it.  It is really a sphygmomanometer—­the little expert witness that never lies—­one of the instruments the insurance companies use now to register blood pressure and discover certain diseases.  It occurred to me that it might be put to other and equally practical uses.  For no one can conceal the emotions from this instrument, not even a person of cast-iron nerves.”

She had placed it on Drummond’s arm.  He appeared fascinated.

“See how it works?” she went on.  “You see one hundred and twenty-five millimeters is the normal pressure.  Kitty Carr is absolutely abnormal.  I do not know, but I think that she suffers from periodical attacks of vertigo.  Almost all kleptomaniacs do.  During an attack they are utterly irresponsible.”

Drummond was looking at the thing carefully.  Constance turned to Annie Grayson.

“Where’s your husband?” she asked offhand.

“Oh, he disappeared as soon as these department store dicks showed up,” she replied bitterly.  She had been watching Constance narrowly, quite nonplussed, and unable to make anything out of what was going on.

Constance looked at Drummond inquiringly.

He shook his head slowly.  “I’m afraid we’ll never catch him,” he said.  “He got the jump on us—­although we have our lines out for him, too.”