Next, associate this rapid appearance and disappearance with the chief symptom of hay fever, the itching, the intolerable itching, of the eyes, nose, and throat, itching that ceases at once on removal from the irritating atmosphere and returns instantly when the irritating atmosphere is reapplied. Turn to the skin, the external mucous membrane. What is that disorder of the skin that appears abruptly, presents redness, swelling, and intense itching, and ceases abruptly after a few minutes or a few hours according to your ability to get rid of the irritating cause,--that can be reproduced any number of times by exposure to the same cause? Why, hives, of course, urticaria or angioneurotic oedema. And a hive (or urticaria or angioneurotic oedema) is not an inflammation. It is a vascular spasm, a spasm of the minute vessels that drain small areas of skin, causing a local stoppage of the circulation in that small area, a turgescence or exudate, the hive. Just as suddenly as it began, the spasm of the vessels may relax, the swollen area is drained rapidly, and the hive disappears, leaving a faint redness. This is exactly the case with hay fever. It is an urticaria, a vascular spasm. The sudden onset in response to a specific irritant and the sudden disappearance--this is no catarrhal inflammation and no rhinitis or inflammation of any kind. Those cases of hives that appear quickly after chilling the skin are perfect analogues of hay fever, appearing in response to the local irritation of odors and dust. There are cases of hay fever that resemble ordinary hives in being aggravated by certain foods, especially strawberries, acid foods, and malt liquors. This has a practical bearing on treatment; for, in such cases, simply excluding these foods from the diet and the administration of an alkali gives relief. Again, many hay fever subjects suffer from urticaria, as in the case reported to me by Dr. Rice of Hawaii, in which the attacks of hay fever alternated with urticaria. Sir Morell Mackenzie was wrong when he said that hay fever "had no pathology because it leaves no permanent structural lesion behind it." Hay fever "has a pathology" if urticaria has a pathology, for urticaria, too, subsides and leaves no traces. However, in this statement, we recognize the effort to state the difference between the evanescent lesions of hay fever and the more persistent lesions of catarrhal inflammation; which is just the difference between an urticaria that comes and goes in half an hour and an eczema (catarrhal dermatitis) that takes several days to develop and is attended by a real inflammatory exudate that requires many days for its absorption.