Any medicament, no matter how valuable, may do great harm if it is employed indiscriminately. The fame of the new antihistaminic drugs has become so widespread, indeed, that they are often prescribed merely to satisfy the patient's curiosity. A critical inventory of their value is therefore indicated. When an antigen to which a patient is sensitive enters his system, certain antibodies called "reagins" are formed, which are responsible for the allergic wheal. Simultaneously a protective antibody may originate, which is thermostabile (Loveless1) and presumably accounts for the improvement of the disease. The combined action of antigen and specific reagin in the bloodstream or in the tissues releases histamine and histamine-like substances which dilate capillary blood vessels and induce smooth muscle spasm, especially bronchospasm. Thus through the action of histamine the allergic wheal is formed—On the skin in urticaria; in the nose and sinuses in hay fever; in the mucous