See Gratiolet on this subject, De la Phys. p. 287. Dr. J. Crichton Browne, from his observations on the insane, is convinced that attention directed for a prolonged period on any part or organ may ultimately influence its capillary circulation and nutrition. He has given me some extraordinary cases; one of these, which cannot here be related in full, refers to a married woman fifty years of age, who laboured under the firm and long-continued delusion that she was pregnant. When the expected period arrived, she acted precisely as if she had been really delivered of a child, and seemed to suffer extreme pain, so that the perspiration broke out on her forehead. The result was that a state of things returned, continuing for three days, which had ceased during the six previous years. Mr. Braid gives, in his ‘Magic, Hypnotism,’ &c., 1852, p. 95, and in his other works analogous cases, as well as other facts showing the great influence of the will on the mammary glands, even on one breast alone. When we direct our whole attention to any one sense, its acuteness is increased;[1340] and the continued habit of close attention, as with blind people to that of hearing, and with the blind and deaf to that of touch, appears to improve the sense in question permanently. There is, also, some reason to believe, judging from the capacities of different races of man, that the effects are inherited. Turning to ordinary sensations, it is well known that pain is increased by attending to it; and Sir B. Brodie goes so far as to believe that pain may be felt in any part of the body to which attention is closely drawn.[1341] Sir H. Holland also remarks that we become not only conscious of the existence of a part subjected to concentrated attention, but we experience in it various odd sensations as of weight, heat, cold, tingling, or itching.[1342] Lastly, some physiologists maintain that the mind can influence the nutrition of parts. Sir J. Paget has given a curious instance of the power, not indeed of the mind, but of the nervous system, on the hair. A lady “who is subject to attacks of what is called nervous headache, always finds in the morning after such an one, that some patches of her hair are white, as if powdered with starch. The change is effected in a night, and in a few days after, the hairs gradually regain their dark brownish colour.”[1343]