11th March, 1949.
Dear Crick,
Thank you for letting me know about your decision.  I expect you are quite right.  If the X-ray diffraction studies of protein are what interest you most, in spite of any deterrent I may have exerted, you can be reasonably sure that your decision is the best one.  My memory only comes back very slowly but I seem to remember now, and it may amuse you, that a year or so ago when Perutz asked me about possible people to join him, I mentioned your name.  If so, I don't regret it in spite of what I said to you.  There is no doubt of the value and importance of the work and I hope that someday it will tie on more closely to the active processes in muscle in which I am interested.  If so, it will be a good thing to have someone mixed up with it who does know something about the properties of living material.  Too often, the biochemists who work on muscle (usually muscles ground up with sand and extracted!) have little idea about the properties of living functioning muscle.  I have tried to persuade Astbury at intervals that living muscles are not quite the same as dried ones; and on the whole he has been fairly teachable.  You, with your year or two at biology, will probably be more susceptible.
Astbury agrees that in X-ray studies of living systems much more powerful equipment is necessary in order to allow shorter exposures.   Perhaps someday that will be available.
Yours sincerely,
A.V. Hill