STUDIES ON THE SENSITIZATION OF ANIMALS WITH SIMPLE CHEMICAL COMPOUNDS VIII. SENSITIZATION TO PICRIC Acre; SvBsn)I~mY AGENTS AND MODE OF SENSITIZATION BY K. LANDSTEINER, M.D., AND A. A. DI SOMMA, PH.D

In sensitization experiments with a fair number (17) of compounds all similar in chemical constitution, namely C1 and NO2 substitution products of benzene, a definite correlation has been found (1, 2) between the capacity to sensitize guinea pigs under given conditions and the ease with which the substituents are replaceable. For example, the labile 2,4-dinitrochloro-benzene proved to be a powerful sensitizing agent whilst the compounds 1,2,4-and 1,4,2-dichloronitrobenzene resistant to treatment with alkali or aniline were ineffective. The demonstration of a correlation between chemical properties and allergic activity led to the detection of new groups of reactive chemicals endowed with sensitizing capacity, namely acyl chlorides and benzyl chlorides. Analogous observations on acid anhydrides have recently been made by Jacobs (3) and his colleagues, and other reac-tive compounds as diazomethane and mustard oil have been added to the list of experimental sensitizers (4). Moreover, the above results were corroborated in human beings by Sulzberger and Baer (5). Here, likewise, 2,4-dinitrochlorobenzene sensitized a considerable percentage of individuals (cf. Haxthausen (6)) and again 1 , 2 , 4-a n d 1,4,2-dichloronitro-benzene failed to do so, with a possible exception in one person. Whereas the connection of sensitizing power and the reactivity of substances under conditions as they may exist in the animal body is well established, there remains the fact, as mentioned previously (2), that compounds which from their chemical character would not appear to enter readily into firm combination with constituents of the animal body, still engender sensitivity in human beings even though not as frequently as certain typical incitants, e.g. dinitrochlorobenzene or urushiol (poison ivy). Indeed, with the latter substances experimental sensitization succeeds almost regularly, a single dose often sufficing to induce hypersensitiveness in man as well as in guinea pigs when applied on the intact skin and,