RE: One of Chekhov's letters in which he wrote about Tolstoy and his concern for his deteriorating health at the same time that Chekhov suffered a marked deterioration in health:

[thename]

Tolstoy was a great man, indeed!
Ana Karenina and War and peace are two of the greatest novels ever written. Less known, but to me even more important is his theoretical work. The Kingdom of God is within you. Life changing stuff...