1970. That truths cannot be apprehended, but are rejected among idle conceits, is evinced by one example which, though a natural verity, would scarcely be believed, to wit, that the least degree of thought and affection produces an effect upon all the organic principles of the brain which are in front of the fibrils, namely, the cortical substances; and because it affects the principles, it affects also all things of the fibers arising from them, which are myriads of myriads, and thus the whole body. Moreover, that of all those myriads, there is no portion of cortical substance, no fiber, no point of a fiber, that is altogether like another, but a continual variety reigns throughout, and thus the whole brain and the whole body with its innumerable varieties constitute one single and most subtle act of our thought, which we indeed suppose to be of infinite subtlety, but which nevertheless consists of countless varieties of persuasion and affection in each minutest point of thought. Yet who would believe these things, when notwithstanding it is simply the statement of a natural truth, which can be demonstrated as well from known philosophy as from manifold experience? - 1748, May 16.