J. soc. cos. CHEM. 15, 285-295 (1964) METHODS FOR EVALUATION OF PRODUCTS DESIGNED FOR ORAL ODOR CONTROL By WILLIAM ilk. CURBY and VINCENT F. LISANTI* Presented September 24-25, 1963, Seminar, Boston, Mass. ABSTRAGT The limitations of the Fair and 'Wells osmoscope instrument are discussed in relation to the physiology and the biophysics of oilaction and the specific and general cases of the Weber-Fechner law. A simple dilution procedure having linear response characteristics and not subject to the range limitation of the Fair and Wells osmoscope is presented, and the results obtained from each technique are com- pared. Recent advances in physical and physico-chemical tech- niques for evaluation of specific compounds in gas and vapor mix- tures have caused them to be considered as methods of choice for the objective analysis of odors. Of the several techniques in develop- ment, those utilizing gas chromatography, infrared densitometry and visual light microdensitometry are discussed and their advantages and limitations considered. Included in these discussions is the evaluation of two new techniques to aid in the determination of the chemical nature of odor producing gases and vapors. One of these is designed to determine the approximate molecular weight of gases in the human breath, while the other is applicable to clinical evaluation of some of the included solvent soluble I•ases. INTRODUCTION It is intended in this paper to consider methods for appraisal of odor. the instrumentation necessary will be considered only as required for the understanding of the methods. The evolution of knowledge about princi- ples involved in the operation of natural systems follows a pattern. Sub- jective information is first obtained, and theories are developed relative to the operation of the system. These theories are usually sufficient to sepa- rate the related physical and chemical changes in the system into those which initiate changes and those which are the results of the changes in the case of physiological functions, into the stimuli and the responses. * I. S. R., Sias Research Laboratories, Brooks Hospital, Brookline, Mass. 02146 285

286 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS When it is possible to control the intensity of the stimulus and also mea- sure the resulting magnitude of the response, sufficient information becomes available to determine how the apparatus of the system operates. If this information is combined with that obtained from gross and microscopic dissection of the organ complex, one is usually able to develop a model which can be studied in the laboratory. It is at this stage in the process of evolution of knowledge that the responses normally expected from a given stimulus can be predicted. We can then prescribe corrective measures to return the system to normal, or we can control a system away from normal if that is our desire. Because it has been possible to measure the stimuli and the responses, we have an understanding of the workings of the systems in the body which detect light, sound, pressure, heat, and, to a lesser degree, solid and liquid chemicals. The advancement of our knowledge of the operation of the sys- tem in the body for the detection of chemicals in the form of gases and vapors has been limited. We have not been able to monitor the responses in the olfactory apparatus directly. The complexity of the olfactory system together with its proximity to the brain have limited our ability to envision a model of the system. The number and ranges of concentration of the stimulants is so great that it has been impossible to determine the operation of the system through a knowledge of its limits. We are faced with a rather unique problem. We have too many stimuli to deal with, too much sensitivity in the organ, too wide an operating range, and too little objective output data to make any analysis of the process of oilaction. We have been required to make appraisals of odors in the intact system, i.e., through the judgments of persons trained to distinguish par- ticular odor signals in odor noise backgrounds that are at times in ratios of less than unity. Two alternative approaches to the detection of odors have been of value in the appraisal of their type and intensity. These are: objective methods and dynamic analytical methods. Within the past ten years, objective methods for the qualitative (and to a more limited extent, quantitative) evaluation of chemicals in gases and vapors have developed rapidly. The applicability of these techniques to the detection of type and magnitude of oral odor will be discussed later. The second approach results from the study of the dynamics of the physiology of sensation in the body. When it is not possible to utilize the method of evaluation, of prin- ciples of operation of a body function as outlined earlier, a study of the dynamics of the system in operation can be undertaken. While it is not possible to obtain exact amounts from a subjective study, it is possible to obtain reliable information from the first derivatives of these values, i.e., while we cannot know from a human judgment an exact value of a particular response, we can obtain accurate information about the rate of change in the response as judged by the subject. This is because the body utilizes