Front Page Titles (by Subject) PASSIONS. Their Influence upon the Body, and that of the Body upon Them. - The Works of Voltaire, Vol. VI (Philosophical Dictionary Part 4)
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PASSIONS. Their Influence upon the Body, and that of the Body upon Them. - Voltaire, The Works of Voltaire, Vol. VI (Philosophical Dictionary Part 4) 
The Works of Voltaire. A Contemporary Version. A Critique and Biography by John Morley, notes by Tobias Smollett, trans. William F. Fleming (New York: E.R. DuMont, 1901). In 21 vols. Vol. VI.
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Pray inform me, doctor—I do not mean a doctor of medicine, who really possesses some degree of knowledge, who has long examined the sinuosities of the brain, who has investigated whether there is a circulating fluid in the nerves, who has repeatedly and assiduously dissected the human matrix in vain, to discover something of the formation of thinking beings, and who, in short, knows all of our machine that can be known; alas! I mean a very different person, a doctor of theology—I adjure you, by that reason at the very name of which you shudder, tell me why it is, that in consequence of your young and handsome housekeeper saying a few loving words, and giving herself a few coquettish airs, your blood becomes instantly agitated, and your whole frame thrown into a tumult of desire, which speedily leads to pleasures, of which neither herself nor you can explain the cause, but which terminate with the introduction into the world of a thinking being encrusted all over with original sin. Inform me, I entreat you, how the action tends to or is connected with the result? You may read and re-read Sanchez and Thomas Aquinas, and Scot and Bonaventure, but you will never in consequence know an iota the more of that incomprehensible mechanism by which the eternal architect directs your ideas and your actions, and originates the little bastard of a priest predestined to damnation from all eternity.
On the following morning, when taking your chocolate, your memory retraces the image of pleasure which you experienced the evening before, and the scene and rapture are repeated. Have you any idea, my great automaton friend, what this same memory, which you possess in common with every species of animals, really is? Do you know what fibres recall your ideas, and paint in your brain the joys of the evening by a continuous sentiment, a consciousness, a personal identity which slept with you, and awoke with you? The doctor replies, in the language of Thomas Aquinas, that all this is the work of his vegetative soul, his sensitive soul, and his intellectual soul, all three of which compose a soul which, although without extension itself, evidently acts on a body possessed of extension in course.
I perceived by his embarrassed manner, that he has been stammering out words without a single idea; and I at length say to him: If you feel, doctor, that, however reluctantly, you must in your own mind admit that you do not know what a soul is, and that you have been talking all your life without any distinct meaning, why not acknowledge it like an honest man? Why do you not conclude the same as must be concluded from the physical promotion of Doctor Bourssier, and from certain passages of Malebranche, and, above all, from the acute and judicious Locke, so far superior to Malebranche—why do you not, I say, conclude that your soul is a faculty which God has bestowed on you without disclosing to you the secret of His process, as He has bestowed on you various others? Be assured, that many men of deep reflection maintain that, properly speaking, the unknown power of the Divine Artificer, and His unknown laws, alone perform everything in us: and that, to speak more correctly still, we shall never know in fact anything at all about the matter.
The doctor at this becomes agitated and irritated; the blood rushes into his face; if he had been stronger than myself, and had not been restrained by a sense of decency, he would certainly have struck me. His heart swells; the systole and diastole are interrupted in their regular operation; his brain is compressed; and he falls down in a fit of apoplexy. What connection could there be between this blood, and heart, and brain, and an old opinion of the doctor contrary to my own? Does a pure intellectual spirit fall into syncope when another is of a different opinion? I have uttered certain sounds; he has uttered certain sounds; and behold! he falls down in apoplexy—he drops dead!
I am sitting at table, “prima mensis,” in the first of the month, myself and my soul, at the Sorbonne, with five or six doctors, “socii Sorbonnici,” fellows of the institution. We are served with bad and adulterated wine; at first our souls are elevated and maddened; half an hour afterwards our souls are stupefied, and as it were annihilated; and on the ensuing morning these same worthy doctors issue a grand decree, deciding that the soul, although occupying no place, let it be remembered, and absolutely immaterial—is lodged in the “corpus callosum” of the brain, in order to pay their court to surgeon La Peyronie.
A guest is sitting at table full of conversation and gayety. A letter is brought him that overwhelms him with astonishment, grief, and apprehension. Instantly the muscles of his abdomen contract and relax with extraordinary violence, the peristaltic motion of the intestines is augmented, the sphincter of the rectum is opened by the convulsions which agitate his frame, and the unfortunate gentleman, instead of finishing his dinner in comfort, produces a copious evacuation. Tell me, then, what secret connection nature has established between an idea and a water-closet.
Of all those persons who have undergone the operation of trepanning, a great proportion always remain imbecile. Of course, therefore, the thinking fibres of their brain have been injured; but where are these thinking fibres? Oh, Sanchez! Oh, Masters de Grillandis, Tamponet, Riballier! Oh, Cogé-Pecus, second regent and rector of the university, do give me a clear, decisive, and satisfactory explanation of all this, if you possibly can!
While I was writing this article at Mount Krapak for my own private improvement, a book was brought to me called “The Medicine of the Mind,” by Doctor Camus, professor of medicine in the University of Paris. I was in hopes of finding in this book a solution of all my difficulties. But what was it that I found in fact? Just nothing at all. Ah, Master Camus! you have not displayed much mind in preparing your “Medicine of the Mind.” This person strongly recommends the blood of an ass, drawn from behind the ear, as a specific against madness. “The virtue of the blood of an ass,” he says, “re-establishes the soul in its functions.” He maintains, also, that madmen are cured by giving them the itch. He asserts, likewise, that in order to gain or strengthen a memory, the meat of capons, leverets, and larks, is of eminent service, and that onions and butter ought to be avoided above all things. This was printed in 1769 with the king’s approbation and privilege; and there really were people who consigned their health to the keeping of Master Camus, professor of medicine! Why was he not made first physician to the king?
Poor puppets of the Eternal Artificer, who know neither why nor how an invisible hand moves all the springs of our machine, and at length packs us away in our wooden box! We constantly see more and more reason for repeating, with Aristotle, “All is occult, all is secret.”