Studies in olfactory acuity. 4. Relative detectability of n-aliphatic acids by the dog

Abstract The ability of two dogs to detect the first eight members of the formic acid series in the vapour phase has been investigated and a behavioural technique for determining the dog's olfactory thresholds is described. In one dog, detectability tended to increase logarithmically as the series is ascended, but in the other this relation is discontinuous: the fifth member is less easily detected than the fourth and higher acids are displaced proportionately in their effects. It is suggested that this anomaly is determined by a corresponding break in the water solubilities of these acids. When expressed as thermodynamic activities the first four acids are detected at decreasing activities as the series is ascended whilst members of intermediate chain length are about equally stimulating. In both dogs reversals are present in the stimulus-response curves which tend to occur at logarithmically decreasing concentrations as the series is ascended. There is no break in this relation. It is concluded that the threshold data presented are not inconsistent with Adrian's suggestion that the sensitivity of individual olfactory receptors is similar in man and dog.