Introduction The hypersensitive state in man, which is clinically expressed as asthma and hay fever, though studied now for nearly twenty years is by no means fully understood. We do not yet know exactly how and why a sensitiveness to one or several particular substances originates and persists in a certain small percentage (about 5 per cent) of the human race.The condition was originally assumed to be anaphylaxis (1) (2), but early studies (3) in asthma and hay fever disclosed facts regarding this type of sensitization in man that were not in entire accord with those that obtain in anaphylaxis. Briefly stated, these facts were: that inherited factors play an important part for they influence the age of onset of clinical sensitization as well as the number to become sensitive among the offspring of sensitive antecedents; that the condition is apparently spontaneous, since clinical sensitization is not obtained by artificial means.
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