Having lamented with you the mournful events which render the name of that disease peculiarly alarming to you, and knowing your friendly solicitude about Mr. ——, I do not wonder at your earnest desire to know something of the nature of a distemper with which he is threatened, and which has proved fatal to so many of our friends. But I am surprised that you have not chosen a more enlightened instructor, when you have so many around you. Though conscious that I have no just claim to all the obliging expressions which your partiality to my opinions has prompted you to make use of, yet I am too much flattered by some of them, to refuse complying with your request. My sentiments, such as they are, will at least have the merit of being clearly understood. I shall observe your prohibition, not to refer you to any medical book; and shall carefully avoid all technical terms, which you so much abominate. With regard to your shewing my Letter to any of the faculty; if you find yourself so inclined, I have not the smallest objection; for those who have the greatest knowledge in their profession, are best acquainted with its uncertainty, and most indulgent to the mistakes or errors of others.
Alas, my friend! how is it possible that physicians should avoid mistakes? If the ablest mechanic were to attempt to remedy the irregular movements of a watch, while he remained ignorant of the structure and manner of acting of some of the principal springs, would he not be in danger of doing harm instead of good? Physicians are in the situation of such a mechanic; for, although it is evident that the nerves are the organs of motion and sensation, yet their structure is not known. Some anatomists assert they are impervious cords; others, that they are slender tubes, containing a fluid. But what the nature of this fluid is; whether it serves only to nourish the nerves themselves, or is the medium by which they convey feeling and the power of motion to other parts, is not ascertained even by those who argue for its existence; far less is it explained in what manner ideas, formed within the brain, can, by the means of solid cords, or by a fluid contained in tubes, communicate motion at pleasure to the legs and arms. We are ignorant why the will, which has no influence over the motion of an animal’s heart, should find the feet obedient to her dictates; and we can no more explain how a man can move one leg over the other by volition, or the mere act of willing, than how he could, by the same means, move Ossa on the top of Olympus. The one happens every moment, the other would be considered as a miracle; but they are equally unaccountable. While parts so infinitely essential to life are not understood, instead of being surprised that so many diseases baffle the skill of the physician, we have more reason to be astonished that any can be alleviated or cured by his art.