Desire, whose face was invisible, took a moment to answer this.  When she did her voice was carefully with-out expression.

“Then this ends my usefulness.  You will not need me any more.”

The professor, who had been nursing his knee on the corner of the desk, straightened up so suddenly that he heard his spine click.

“What’s this?” he said. (Good heavens—­the girl was as full of surprises as a grab-bag!)

“It was for the book you needed me, was it not?  That was my share of our partnership.”

("Now you’ve done it!” shouted an exultant voice in the professor’s brain.  “Oh, you are an ass!”)

“Shut up!” said Spence irritably.  “I wasn’t talking to you,” he explained apologetically.  “It’s just a horrid little devil I converse with sometimes.  What I meant was—­” He did not seem to know what he meant and looked rather helplessly out of the window.  “Oh, I say,” he said presently, “you are not going to—­to act like that, are you?  Agitation’s so frightfully bad for me.  Ask old Bones.”

“You are not agitated,” said Desire coldly.  “Please be serious.”

“I am.  Deuced serious.  And agitated too.  You ought to think twice before you startle me like that—­just when everything was going along so nicely.”

“I am only reminding you of your own agreement,” stubbornly.  “I want to be of use.”

“Very selfish of you.  Can’t you think of someone else once in a while?”

“Selfish?  Because I want to help?”

“Certainly.  I wonder you don’t see it!  Think of the mornings I’ve put in on this dashed book just because you wanted to help.  I have to be polite, haven’t I?—­up to a point.  But when you begin to blame me for doing poorly what I do not want to do at all I begin to see that my self-sacrifice is not appreciated.”

“You are talking nonsense.”

“Perhaps I am.  But it was you who started it.  When you said I did not need you, you said a very nonsensical thing.  And a very unkind thing, too.  A man does not like to talk of—­his need.  But, now that we have come to just this point, let us have it out.  Surely our partnership was not quite as narrow as you suggest?  The book is a detail.  It is L. part of life which will fit in somewhere—­an important part in its right place—­but it isn’t the whole pattern.”  He smiled whimsically.  “Do not think of me as just an animated book, my dear—­if you can help it.  And remember, no matter how we choose to interpret our marriage, you are my wife.  And my very good comrade.  The one thing which could ever change my need of you is your greater need of—­of someone else.”

The last words were casual enough but the look which accompanied them was keen, and a sense of relief rose gratefully in the professor as no sign of disturbance appeared upon the thoughtful face of his hearer.