The biological sense of smell: olfactory search behavior and a metabolic view for olfactory perception

Part I of the thesis describes the olfactory searching and scanning behaviors of rats in a wind tunnel, and a detailed movement analysis of terrestrial arthropod olfactory scanning behavior. Olfactory scanning behaviors in rats may be a behavioral correlate to hippocampal place cell activity.

Part II focuses on the organization of olfactory perception, what it suggests about a natural order for chemicals in the environment, and what this in tum suggests about the organization of the olfactory system. A model of odor quality space (analogous to the "color wheel") is presented. This model defines relationships between odor qualities perceived by human subjects based on a quantitative similarity measure. Compounds containing Carbon, Nitrogen, or Sulfur elicit odors that are contiguous in this odor representation, which thus allows one to predict the broad class of odor qualities a compound is likely to elicit. Based on these findings, a natural organization for olfactory stimuli is hypothesized: the order provided by the metabolic process. This hypothesis is tested by comparing compounds that are structurally similar, perceptually similar, and metabolically similar in a psychophysical cross-adaptation paradigm. Metabolically similar compounds consistently evoked shifts in odor quality and intensity under cross-adaptation, while compounds that were structurally similar or perceptually similar did not. This suggests that the olfactory system may process metabolically similar compounds using the same neural pathways, and that metabolic similarity may be the fundamental metric about which olfactory processing is organized. In other words, the olfactory system may be organized around a biological basis.

The idea of a biological basis for olfactory perception represents a shift in how olfaction is understood. The biological view has predictive power while the current chemical view does not, and the biological view provides explanations for some of the most basic questions in olfaction, that are unanswered in the chemical view. Existing data do not disprove a biological view, and are consistent with basic hypotheses that arise from this viewpoint.

A colorimetric determination of hydrocyanic acid

The object of this investigation is to devise a rapid, fairly accurate, colorimetric analysis for HCN to be used in field work for determining instantaneous concentrations of the gas under fumigating canvas. A large amount of money is expended yearly by the citrus industry of this state in attempting to control and to eradicate the scale pests. Although fumigation with HCN has been practiced tor many years, the progress made has been anything but satisfactory. The greater portion of the work has always been carried on by contractors, who in a large number of cases have been very unscrupulous. The materials and labor are very expensive and the growers have been satisfied to adhere to beaten paths and hope for the best results on scale kill with the least attendant foliage injury. One familiar with fumigating, either from the grower's or the operator's viewpoint, knows that very widely varying results are obtained, even under what are apparently identical condition. Even after discounting for the dishonesty of some operators and the prejudices of the grower, there is still a large variance between desired or expected results and those actually obtained.