The term "allergy" means a condition of unusual or exaggerated specific hypersensitivity to a substance which, under like conditions and in similar amounts, is harmless for the large majority of members of the same species. Allergic diseases are divided by Coca1 into these four classifications: "(1) atopy (hay fever, asthma, eczema group), (2) contact dermatitis, (3) serum allergy, and (4) drug allergy." More than one type may be present in the same individual as well as among members of his family.
Bray2 has diagramed the integral factors producing the allergic state and listed the methods of entry of the specific antigens, allergens or causative agents by the following routes: "(1) inhalation, (2) ingestion, (3) injection, (4) infection and (5) contact." Catalyzing nonspecific factors, he stated further, are "(1) dietary, (2) environmental, (3) nasal, (4) toxic, (5) psychic, (6) endocrine, (7) physical, (8) chemical and (9) mechanical." Hereditary predisposition
DANIEL RK. ALLERGY AND CATARACTS. JAMA. 1935;105(7):481-483. doi:10.1001/jama.1935.02760330007002