The Professor nipped the last joint between his finger and thumb for a moment till it was black at the end; then he turned to the saucer at his side, which Hilda herself had placed there, and chose from it, cat-like, with great deliberation and selective care, a particular needle.  Hilda’s eyes followed his every movement as closely and as fearlessly as ever.  Sebastian’s hand was raised, and he was just about to pierce the delicate white skin, when, with a sudden, quick scream of terror, she snatched her hand away hastily.

The Professor let the needle drop in his astonishment.  “What did you do that for?” he cried, with an angry dart of the keen eyes.  “This is not the first time I have drawn your blood.  You knew I would not hurt you.”

Hilda’s face had grown strangely pale.  But that was not all.  I believe I was the only person present who noticed one unobtrusive piece of sleight-of-hand which she hurriedly and skilfully executed.  When the needle slipped from Sebastian’s hand, she leant forward even as she screamed, and caught it, unobserved, in the folds of her apron.  Then her nimble fingers closed over it as if by magic, and conveyed it with a rapid movement at once to her pocket.  I do not think even Sebastian himself noticed the quick forward jerk of her eager hands, which would have done honour to a conjurer.  He was too much taken aback by her unexpected behaviour to observe the needle.

Just as she caught it, Hilda answered his question in a somewhat flurried voice.  “I—­I was afraid,” she broke out, gasping.  “One gets these little accesses of terror now and again.  I—­I feel rather weak.  I don’t think I will volunteer to supply any more normal blood this morning.”

Sebastian’s acute eyes read her through, as so often.  With a trenchant dart he glanced from her to me.  I could see he began to suspect a confederacy.  “That will do,” he went on, with slow deliberateness.  “Better so.  Nurse Wade, I don’t know what’s beginning to come over you.  You are losing your nerve—­which is fatal in a nurse.  Only the other day you let fall and broke a basin at a most critical moment; and now, you scream aloud on a trifling apprehension.”  He paused and glanced around him.  “Mr. Callaghan,” he said, turning to our tall, red-haired Irish student, “Your blood is good normal, and you are not hysterical.”  He selected another needle with studious care.  “Give me your finger.”

As he picked out the needle, I saw Hilda lean forward again, alert and watchful, eyeing him with a piercing glance; but, after a second’s consideration, she seemed to satisfy herself, and fell back without a word.  I gathered that she was ready to interfere, had occasion demanded.  But occasion did not demand; and she held her peace quietly.