“My illness is life itself.”

Science - The Endless Frontier (1945)
Context: Science, by itself, provides no panacea for individual, social, and economic ills. It can be effective in the national welfare only as a member of a team, whether the conditions be peace or war. But without scientific progress no amount of achievement in other directions can insure our health, prosperity, and security as a nation in the modern world.

The Aquarian Conspiracy (1980), Chapter Three, Brains Changing, Minds Changing

Source: The Sense of an Ending

Source: The Hungering Dark

From a note Twain wrote in London on May 31, 1897 to reporter Frank Marshall White: Shelley Fisher Fishkin, Lighting Out For the Territory : Reflections on Mark Twain and American Culture (Oxford University Press, 1996), p. 134 http://books.google.com/books?id=ms3tce7BgJsC&lpg=PA134&vq=%22the%20report%20of%20my%20death%20was%20an%20exaggeration%22&pg=PA134. (The original note is the Papers of Mark Twain, Accession #6314, etc., Clifton Waller Barrett Library, Special Collections, University of Virginia Library, Charlottesville, Va. http://ead.lib.virginia.edu/vivaxtf/view?docId=uva-sc/viu00005.xml, in Box 1.)
White subsequently reported this in "Mark Twain Amused," New York Journal, 2 June 1897. White also recounts the incident in "Mark Twain as a Newspaper Reporter," The Outlook, Vol. 96, 24 December 1910
"Chapters from My Autobiography", The North American Review, 21 September 1906, p. 160. Mark Twain
Misquote: The reports of my death are greatly exaggerated.
This paraphrase or misquote may be more popular than the original.
Variant: I said - 'Say the report is greatly exaggerated'.

Kulturphilosophie (1923), Vol. 2 : Civilization and Ethics
Context: Reverence for life, veneratio vitæ, is the most direct and at the same time the profoundest achievement of my will-to-live.
In reverence for life my knowledge passes into experience. The simple world- and life-affirmation which is within me just because I am will-to-live has, therefore, no need to enter into controversy with itself, if my will-to-live learns to think and yet does not understand the meaning of the world. In spite of the negative results of knowledge, I have to hold fast to world- and life-affirmation and deepen it. My life carries its own meaning in itself. This meaning lies in my living out the highest idea which shows itself in my will-to-live, the idea of reverence for life. With that for a starting-point I give value to my own life and to all the will-to-live which surrounds me, I persevere in activity, and I produce values.

Maxim 124
Sentences, The Moral Sayings of Publius Syrus, a Roman Slave

Source: The Black Obelisk

Source: A Portrait of the Artist as a Young Man