Then there are other superficial symptoms--"

"Good heavens!" broke in Harren; "how can you prove a man to be in love
when he himself doesn't know whether he is or not? If a man isn't in
love no Bertillon system can make him so; and if a man doesn't know
whether or not he is in love, who can tell him the truth?"

"I can," said the Tracer calmly.

"What! When I tell you I myself don't know?"

"_That_," said the Tracer, smiling, "is the final and convincing
symptom. _You_ don't know. _I_ know because you _don't_ know. That is
the easiest way to be sure that you are in love, Captain Harren, because
you always are when you are not sure. You'd know if you were _not_ in
love. Now, my dear sir, you may lay your case confidently before me."

Harren, unconvinced, sat frowning and biting his lip and twisting his
short, crisp mustache which the tropical sun had turned straw color and
curly.

"I feel like a fool to tell you," he said. "I'm not an imaginative man,
Mr. Keen; I'm not fanciful, not sentimental. I'm perfectly healthy,
perfectly normal--a very busy man in my profession, with no time and no
inclination to fall in love."

"Just the sort of man who does it," commented Keen. "Continue."

Harren fidgeted about in his chair, looked out of the window, squinted
at the ceiling, then straightened up, folding his arms with sudden