1970. It was said that truths cannot be learned, either, and are therefore rejected as theories. Take, for example, just this one truth, which hardly anyone would believe, when yet it is a truth of nature: That the least thought and feeling touches all the organic beginnings of the brain that form the heads of the fibrils, namely, the cortical substances. And because it touches those very beginnings, it also affects all of the fibrils arising from those beginning ones, which number myriads of myriads-therefore the whole body. Also, that of those myriads, not a single cortical substance, not a single tissue, nor a single particle of a tissue, is entirely like another, but that there is a constant variation, so that the whole brain and the whole body, with all their countless differing parts, is involved in just one single, tiniest interval of our thought, which we suppose to be refined to the uttermost degree, when yet each and every particle of thought is composed of innumerable varieties of persuasion and feeling. Who would believe all this, when yet it is merely a truth of nature that can be demonstrated both by familiar philosophy and by experiments? 1748, 16 May.