mix.[1] He believes, on the basis of his own experiments, that if dissimilar odors of different intensities are mixed, the weeaker odor will cancel part of the odor of the stronger, and will itself be lost, and that if dissimilar odors of the same intensity are mixed, both will disappear or will give but a feeble indeterminate fusion.[2] Zwaardemaker does mot, as alleged by Nagel, adduce his conclusions in regard to mixture as a buttress to his localization and irradiation theory, though he does seek to explain the facts. of mixture and compensation, as he understands them, in harmony with this theory.[3] Nagel, as opposed to Zwaardemaker, believes, on the basis of his own experiments, that any two smells will unite in a mixture which for an instant, at least, will make a simple impression of new quality.[4] He has never found an instance of complete “compensation,” but he agrees with Zwaardemaker that a mixture of several smells is in general weaker than its individual components, and that some combinations of strongly odorous substances are almost odorless.[5] Nagel offers no explanation of the phenomenon of compensation, nor does Zwaardemaker explain it satisfactorily even on the basis of his irradiation-theory. Perhaps it is safe to conclude that most smells will mix. As Nagel suggests, there is no occasion in the perfume trade to mix nauseating or hircine smells with the odors of flowers, spices and resins.
A fourth and final reason for believing that there are not as many simple odors as there are unmixed substances, is that many simple substances have been found by experiment to have composite odors. Chlorphenol and nitrobenzol are good examples of such substances.[6]
Now, if there are a limited number of specific energies of smell, and if most smells are mixed, our ignorance of the elementary smells, and our consequent inability to isolate them, have serious consequences for the value of olfactometric work. This will be clearer if we consider the two methods which are used to discover whether a smell is simple or composite. The method of Passy consists in gradually increasing the dilution of odorous substances, and depends upon the principle that since the stimulus-limina of different odors are different, they must disappear successively as the intensities of the different stimuli are diminished equally.[7] However, it is at least possible that
