The doctor was little impressed by the reproach. “Humph!” he grunted. “Well, suppose you stop nibbling at your hair”—Julia’s braid flew back over her shoulder—“and consider that, when you put your fingers in your mouth, you may be putting in, also, a particle of everything that your fingers have touched. And in Charley’s room there might be jerrums, as Twinkles calls them, from his mouth which would be dangerous. Rehearsal at noon tomorrow.” Expectant curiosity brought the children early to the playroom whither they found that the Health Master had preceded them. “When’s it going to begin?” asked Bettina. “Presently,” replied the master of ceremonies. “We’re going to pretend that this is Charley’s room. Just at present I’m busy with some work.” He shook a notebook at them. “Go ahead and amuse yourselves till I get through.” Julia the observant noted three hues of crayon on the stand beside the doctor. “Are you going to make a sketch?” she inquired. “Never you mind. You attend to your affairs and I’ll attend to mine.” “Dr. Strong is a-goin’ to make a picture of a jerrum,” Bettina informed her favorite doll, Susan Nipper, imprinting a fervent kiss on the pet’s flattened face. “Come on an’ let’s read the paper.” Dr. Strong made a note in his book, with a pencil. “Want to play catch, Junkum?” suggested Bobs to his twin. “All right,” said Julia, seizing upon a glove, while Bobs, in his rôle of pitcher, professionally moistened the ball. Dr. Strong made another note. For half an hour they disported themselves in various ways while the Health Master, whose eyes were roving everywhere, made frequent entries in his book. “All out now,” he ordered finally. “Come back in five minutes.” Before the time was up, they were clustered at the door. Dr. Strong admitted them. “Does the rehearsal begin now?” asked Bobs. “It’s all over,” said the physician. “Look around you.” “Ow-w-w!” wailed Bettina. “Look at Susan Nipper’s nose!” That once inconspicuous feature had turned a vivid green. “And the baseball is red,” cried Bobs. “So’s my glove,” announced Julia. Walking over to her, the Health Master caught her left hand and smeared it with blue crayon. For good measure he put a dab on her chin. “My story-book is all blue, too,” exclaimed the girl. “What’s it for?” “Just by way of illustration,” explained the doctor. “The mouths of all of us contain germs of one kind or another. So I’ve assumed that Bob’s mouth has red, and Junkum’s blue, and Miss Twinkle’s green. Every chalk mark shows where you’ve spread your germs.” “Then the red on the ball is where I wet my fingers for that in-curve,” said Bobs. “And on my glove is where I caught it,” said Julia. “But what’s the blue doing on my left hand?” “I know,” announced Bobs triumphantly. “You got that slow drop on the end of your finger and jammed your finger in your mouth.” “It hurt,” defended Julia. “Look at the walls—and the Indian clubs—and the chair.”