"I believe I am not interested to know whether Vivisection produces results that are profitable to the human race or doesn't. To know that the results are profitable to the race would not remove my hostility to it. The pains which it inflicts upon unconsenting animals is the basis of my enmity towards it, and it is to me sufficient justification of the enmity without looking further. It is so distinctly a matter of feeling with me, and is so strong and so deeply-rooted in my make and constitution, that I am sure I could not even see a vivisector vivisected with anything more than a sort of qualified satisfaction. I do not say I should not go and look on; I only mean that I should almost surely fail to get out of it the degree of contentment which it ought, of course, to be expected to furnish."
-Mark Twain in a letter to the London Anti-Vivisection Society, May 26, 1899
See this Vegan Soapbox article for more information and links to anti-vivisection sites.