Miss Parvati - My sincere apologies! I can only plead ignorance and my gender bias as regards to this site.

The quotation was from Fawn Brodie's biography of Burton, The Devil Drives, page 44. Unfortunately, she does not cite the source.

Carl - I agree, some people do seem to be naturally more able to learn languages, but I have seen some remarkable results from people who were just plain stubborn, the kind who are determined to put their head through a linguistic wall.