BIOASSAY OF CONTACT ALLERGENS 161 allergen increase the sensitization rate, and (c) previous irritation makes a skin site more agreeable for the induction of sensitivity (13-15). The tech- nique of administering allergen under occlusion to the guinea pig was intro- duced by Buehler (16). Numerous studies in man and experimental animals have demonstrated that occlusion renders the barrier layer of the skin more permeable. Clearly, the test method for the evaluation of putative contact allergens that is proposed here requires extensive evaluation to determine its useful- ness. In a limited experience we have found it reliable. It should be empha- sized that it is particularly suited for rating the allergic potential of unknown against known materials, especially where all are designed for the same final use. For example, a proposed topical antibiotic for a given purpose would be compared with two or more topical antibiotic preparations that are currently used for that purpose. Of course, all preparations would be studied, in differ- ent guinea pigs, at the same time. The results of such studies would then not give absolute ratings, but would imply a greater or lesser risk of sensitization by the unknown as compared to the known. With experience, certain likely extrapolations could be made between results of individual experiments. Experience in other laboratories will doubtless improve our method. For instance, it may be that extensive shaving of the sensitization site is unneces- sary and, in fact, that only clipping of the site is necessary. We have no ex- periments directly to that point. (Received October 16, 1972) PREFERENCES (1) Rostenberg, A., and Haeberlin, J. B., Studies in eczematous sensitizations. III. The development in species other than man or the guinea pig, J. Invest. Dermatol., 15, 233-47 (1950). (2) Asherson, G. L., and Ptak, W., Contact and delayed hypersensitivity in the mouse. I. Active sensitization and passive transfer, Immunolog!t, 15, 405-16 (1968). (3) Simon, F., Observations on poison ivy hypersensitiveness in guinea pigs, J. Immunol., 30, 275-86 (1936). (4) Chase, M. W., H!lpersensitivity to Simple Chemicals, Harvey Lecture Series 61, 1965-1966, Academic Press, New York, 1967, pp. 169-203. (5) Marzulli, F. N., Carson, T. R., and Maibach, H. I., Delayed contact hypersensitivity studies in man and animals, Proc. Joint Conf. Cosmet. Sci., Washington, D.C., 107--22 (1968). (6) Magnusson, B., and Kligman, A.M., Allergic Contact Dermatitis in the Guinea Pig, Charles C. Thomas, Springfield, Illinois, 1970. (7) Draize, J. H., Woodward, G., and Calvery, H. O., Methods for the study of irritation and toxicity of substances applied to the skin and mucous membranes, J. Pharmacol. Exp. Ther., 82, 377-90 (1944). (8) Epstein, E., Allergy to dermatologic agents, J. Amer. Med. Ass., 198, 517-20 (1966). (9) Maguire, H. C., and Chase, M. W., Exaggerated delayed-type hypersensitivity to simple chemical a]lergens in the guinea pig, J. Invest. Dermatol., 49, 460-8 (1967). (10) Maguire, H. C., and Chase, M. W., Studies on the sensitization of animals with simple chemical compounds. XIII. Sensitization of guinea pigs with picric acid, J. Exp. Med., 135, 357-75 (1972).

162 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (11) Magnusson, B., and Kligman, A.M., The identification of contact allergens by ammal sasay. The guinea pig maximization test, J. Invest. Dermatol., 52, 268-76 (1969). (12) Maguire, H. C., Jr., Mechanism of intensification by Freund's complete adjuvant of the acquisition of delayed hypersensitivity in the guinea pig, ImmunoL Commun., 1, 239--46 (1972). (13) Landsteiner, K., and Chase, M. W., Studies on the sensitization of animals with simple chemical compounds. VII. Skin sensitization by intraperitoneal injection, J. Exp. Med., 71, 237-45 (1940). (14) Landsteiner, K., and Jacobs, J., Studies on the sensitization of animals with simple chemicals, Ibid., 61, 643-56 (1935). (15) Landsteiner, K., and DiSomma, A. A., Studies on the sensitization of ani•nals with simple chemical compounds. VIII. Sensitization to picric acid subsidiary agents and mode of sensitization, Ibid., 72, 361-6 (1940). (16) Buehler, E. U., Delayed contact dermatitis in the guinea pig, Arch. Dermatol., 91, 171-5 (1965).