The shops gave her none of the acquisitive pleasure he had expected.  To her they were interesting as museums might have been.  She could not, she did not see the use of them.  The women thronging the windows and departments of a great store through which they walked roused her to excited comment.

“What are they buying them all for?” she said, looking at the hats and frocks and the purchasers.  “They have such nice ones already.”

The doctor asked her if she did not think they were very pretty when he had got over his amusement at the idea of women only buying things because they needed them.

“Oh beautiful!” she cried rapturously.  “But you couldn’t do very much in frocks like that.”

“That’s the idea, of course,” said the doctor, watching her quizzically.  “If you only knew it, Marcella, all these shops are built upon a foundation of what your professor calls ‘questing cells.’  You see—­but let’s get out into the air.  You’ve started my bee buzzing now.”

They faced about and elbowed their way through an eager-eyed, aimless-footed throng by the doorway.

“Now go on,” said Marcella when they were in the street, walking down beside Liberty’s.  She had one eye on the windows and one ear for the doctor.

“You see, all these women here—­they’re doing something quite unconsciously when they buy pretty clothes and spend so much time and money on making themselves look so bonny,” said the doctor, striding along in his Inverness cape, quite oblivious that he was a very unique figure in Regent Street.  “They’ll worry tremendously about what colour suits them, what style sets off their beauty best.  I don’t think that it’s really because they like to see something bonny every time they look in their mirror.  I don’t think it’s even that they want admiration, or envy.  It’s simply that they’re ruled by the law of reproduction, if they only knew it.  Inside them is new life—­these same questing cells.  These cells can only find separate existence through complementary cells.  So they urge these women on to make themselves charming, capturing—­married or single, they are the same, deep down, for natural laws take no count of marriage laws, you know.  The men are the same, too.  They beg and placate—­and all the time deep down, they think they are the choosers, the overlords.  And the women tempt them and then run away.  Last of all they yield.  These cells have it ingrained in them that the woman-thing is only ready to yield after a chase.  Very few people do this consciously.  A few do—­people who have been let into the secret of studying natural laws.  Then they either do it for the fun of the chase, or else because they’re too morally lazy to fight the urge of the cells.  That’s when they get holes torn in them.”

He walked on for a few steps, and then turned to laugh into Marcella’s puzzled face.

“All of which, I’d like to point out, I take no credit for, Marcella.  I got it out of Kraill’s Edinburgh lectures that have just been published in book form.”