speak during the operation, its opinion might not accord with that of the physiologist. [A] A Text-book of Human Physiology, designed for the use of Practitioners and Students of Medicine, by Austin Flint, Jr., M. D. D. Appleton & Co. New York: 1876 (page 722). [B] Page 738. [C] Page 585. [D] Page 710. [E] Page 403. [F] Pages 269-70. [G] Page 282. [H] Page 489. [I] Page 629. [J] Page 463. [K] Pages 470-71. There is one experiment in regard to which the severe characterization of English scientists is especially applicable, from the pain necessarily attending it. Numerous investigators have long established the fact that the great sensory nerve of the head and face is endowed with an exquisite degree of sensibility. More than half a century ago, both Magendie and Sir Charles Bell pointed out that merely exposing and touching this fifth nerve gave signs of most acute pain. "All who have divided this root in living animals must have recognized, not only that it is sensitive, but that its sensibility is far more acute than that of any other nervous trunk in the body."[A] "The fifth pair," says Professor John C. Dalton, "is the most acutely sensitive nerve in the whole body. Its irritation by mechanical means _always causes intense pain_, and even though the animal be nearly unconscious from the influence of ether, any severe injury to its large root is almost invariably followed by cries."[B] Testimony on this point is uniform and abundant. If science speaks anywhere with assurance, it is in regard to the properties of this nerve. Yet every year the experiment is repeated before medical classes, simply to demonstrate accepted facts. "This is an operation," says Professor Flint, referring to the division of this nerve, "that we have frequently performed with success." He adds that "it is difficult from the fact that one is working in the dark, and it requires a certain amount of dexterity, _to be acquired only by practice_." Minute directions are therefore laid down for the operative procedure, and illustrations given both of the instrument to be used, and of the head of a rabbit with the blade of the instrument in its cranial cavity.[C] Holding the head of our rabbit firmly in the left hand, we are directed to penetrate the cranium in a particular manner. "Soon the operator feels at a certain depth that the bony resistance ceases; he is then on the fifth pair, and the cries of the animal give evidence that the nerve is pressed upon." This is one of Magendie's celebrated experiments; perhaps the reader fancies that in its modern repetitions the animal suffers nothing, being rendered insensible by anaesthetics? "_It is much more satisfactory to divide the nerve without etherizing the animal, as the evidence of pain is an important guide in this delicate operation._" Anaesthetics, however, are sometimes used, but not so as wholly to overcome the pain.