In a minority of patients with asthma, hay-fever, urticaria, eczema and other manifestations of allergy, the source of the illness can be traced definitely to contact with some material substance to which the patient is sensitive—substances such as pollen, dander, foods, drugs and vapors. In a majority of cases, however, the primary source of the disorder cannot be found even after a most painstaking effort has been made through the use of history, physical examination, skin tests and clinical tests. In a previous paper, I1described a case of urticaria caused specifically and solely by the action of light; in fact, solely by the rays of light at the violet end of the spectrum. Later I found a case identical to this in every respect except for the fact that the urticarial rash was caused solely and specifically by the action of cold; in fact, best by cold between