Need help remembering CS Lewis Quote about Joy and Chemical Reactions I know that there is a line by CS Lewis where he is talking about secular atheists have to try to forget their philosophy in order to find joy in life. The line goes something like... 

"But insofar as... you go from having a good time to having a great time... you must remember that love is merely a chemical reaction."

There might also be a part about his wife, and how his love for her was nothing but a chemicial reaction if we presume that the secularist worldview is correct.

If someone could give me the quote along with perhaps a reference to where it came from I would be very grateful.
There's this passage on page 76 of Present Concerns:


  You can't, except in the lowest animal sense, be in love with a girl if you know (and keep on remembering) that all the beauties both of her person and of her character are a momentary and accidental pattern produced by the collision of atoms, and that your own response to them is only a sort of psychic phosphorescence arising from the behaviour of your genes. You can’t go on getting any very serious pleasure from music if you know and remember that its air of significance is pure illusion, that you like it only because your nervous system is irrationally conditioned to like it. You may still, in the lowest sense, have a ‘good time’; but just in so far as it becomes very good, just in so far as it ever threatens to push you on from cold sensuality into real warmth and enthusiasm and joy, so afar you will be forced to feel the hopeless disharmony between your own emotions and the universe in which you really live.


This is quoted by Tim Keller on page 141 of The Reason for God.