She turned away to answer one of the subordinates, and, at the same
time, Dr. Surtaine was called aside by a man with a shipping-bill.
Looking down the line of workers, Hal saw that each one was simply
opening, reading, and marking with a single stroke, the letters from a
distributing groove. To her questioner Milly Neal was saying, briskly:

"That's Three and Seven. Can't you see, she says she has spots before
her eyes. That's stomach. And the lameness in the side is kidneys. Mark
it 'Three pass to Seven.' There's a combination form for that."

"What branch of the work is this?" asked Hal, as she lifted her eyes to
his again.

"Symptom correspondence. This is the sorting-room."

"Please explain. I'm a perfect greenhorn, you know."

"You've seen the ads. of course. Nobody could help seeing them. They all
say, 'Write to Professor Certain'--the trade name, you know. It's the
regular stock line, but it does bring in the queries. Here's the
afternoon mail, now."

Hundreds upon hundreds of letters came tumbling from a bag upon the
receiving-table. All were addressed to "Prof." or "Dr." Certain.

"How can my father hope to answer all those?" cried Hal.

The girl surveyed him with a quaint and delicious derision. "He? You
don't suppose he ever sees them! What are _we_ here for?"