INHERENT INVALIDITY OF ODOR CLASSIFICATION 27 these relations the same for all? Will they still be the same for those who shall come after us ?" Now, how is it possible to deter- mine objectivity when the observa- tion is one based exclusively on a subjective sensory impression? It is an established scientific method to determine objectivity by the veri- fication of results a fact, or a rela- tionship between facts, is established in the minds of so many normal human beings that it can be said to exist in the nature of the things be- ing observed. "Science," states H. E. Bliss (11), "is distinguished from com- munal, common, or 'common-sense' knowledge and thought in that it is o verified. . Its verification de- pends on rational and technical methods, on evidence, and on com- munal acceptance or consensus." (Emphasis in original.) And the same author (12), else- where: "The verification of 'the data and relations and the validity of the generalizations and law de- pend logically on the constancy of natural law, but intellectually on a consensus of minds accepting those truths ahd theories." (Emphasis in original.) The judgments that are formed on the basis of the classification of facts, stressed Pearson (13), must be "independent of the idiosyn- crasies of the individual mind." Referring to the specific problem of classifying human knowledge, the American philosopher and edu- cator, John Dewey (14), stated that such a classification "can be se- cured only as the intellectual, or conceptual, organization is based upon the order inherent in the fields of knowledge, which in turn mirrors the order of nature." How is one to determine that the order of classification is inherent in the fields of study? The key to the answer to this question is supplied by Pearson (15): "The observations and experiments of science should be repeated as often and by as many observers as possible, in order to ensure that we are dealing with what has validity for all normal hu- man beings, and not with the results of an abnormal perceptive faculty. It is not only, however, in experi- ments or observations which can be repeated easily, but still more in those which it is very difficult or impossible to repeat, that a great weight of responsibility lies upon the recorder and the public which is called upon to accept his results." A scientific concept is thus founded on common acceptance or consensus, based on the verified observations of different human beings. "When one turns to the magnificent edifice of the physical sciences," wrote William James (16), one "sees how it was reared what thousands of disinterested moral lives of men lie buried in its mere foundations what patience and postponement, what choking down of preference, what sub- mission to the icy laws of outer fact were wrote into its very stones and mortar how absolutely impersonal it stands in its vast augustness." From these accepted tenets of

28 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS scientific methodology, one can con- clude that no system in science is valid unless it can be verified and reproduced, by the same individuals and by others. It follows, then, that any effort at classification in a field of knowledge, if it is based ex- clusively on perceptions and obser- vations which inevitably vary with the individual observer, must be inherently invalid. III Efforts to classify odors into qualitative groups are as old as the literature of perfumery. The Greek botanist, Theophrastos (17), re- ferring to those who had studied sensory classification, complained that "with colors they distinguish white and black, and with flavors sweet and bitter, yet they make no corresponding classification of smells, but merely classify them as 'pleasant' or 'unpleasant.'" Theophrastos (18) himself recog- nized the limitations of odor classi- fication, when he wrote, further: "We speak of an odor as pungent, poiverful, faint, sweet, or heavy, though some of these descriptions apply to evil-smelling things as well as to those which have a good odor." A large number of odor classifica- tion systems was created in the years that followed, and they can roughly be divided into two main groups: the systems of those like Linnaeus (19), Zwaardemaker (20), Rimmel (21), and many others, in which several odors were brought together and-simultaneously placed in a single group and those created by Henning and by Crocker and Henderson, in which a single odor was simultaneously placed, in vary- ing degree, in several groups. Zwaardemaker (20), for example, divided all odors into nine cate- gories, which he named as follows: ethereal, aromatic, fragrant, am-' brosiacal, atliaceous, empyreumatic, hircine, putrid, and nauseating. Within each, there could be sub- divisions the aromatic group, for instance, contained five subgroups, named camphoraceous, spicy, anise- thyme, lemon-rose, and almond. But Linnaeus (19) found that there were seven groups Fourcroy (22) that there were five Hailer (23), three Lorry (24), five (entirely different from the five of Fourcroy) and Rimmel (21), eighteen. No two independent researchers who have studied this question have ever arrived at the same or es- sentially similar results. The his- tory of odor classifications of the Linnaeus - Zwaardemaker - Rimmel type indisputably demonstrates an utter lack of reproducibility so far as numbers of classes, names of classes, and the placing of individual odors within the classe• are con- cerned. Every serious student of odor classification had to reject all pre- vious systems, work out a system according to his own subjective olfactory reactions, and his system was destined to be rejected by all serious workers following him. The historical review of odor classifi- cation demonstrates the lack of consensus which is considered