Abstract
Employing thc classical conditioned reflex as an experimental method, the author intended to clarify the olfactory acuity of a dog.
As a test odor, clove oil, which is a non-meaningfull smell for dogs, was used. It was diluted by propylen glycol into various concentrations.
At first, a method to obtain salivatory conditioned reflex by clove oil odor was established. By this method the following results were obtained :
1) Olfactory threshold of a dog for clove oil was 10-7mg/cc. This is million times lower than the olfactory threshold of man.
2) The diluted solution of clove oil and propylen glycol itself were presented to a dog for olfactory discrimination. When the clove oil was highly diluted, the conditioned salivatory reflex of the dog became very irregular to the two solutions. But when a third and very dissimilar odor was presented together with the diluted clove oil or propylen glycol, the dog showed salivation regularly to the clove oil solution and the propylen glycol itself, but not to the dissimilar odor.
3) Beside the measurement of salivation, recording of respiration was found to be very useful for the study of the discriminative ability.
4) It is conjectured that there are mainly three factors involved in the olfactory discriminative processes of a dog, that is, quantity, quality and odor patterns formed by combinations of odor substances.
It is conceivable that a dog discriminates odors by taking advantage of the most useful factor among the above three.
In some cases, a dog may make use of two or more factors in combination. Consequently, it may be said that the olfactory threshold of a dog changes depending upon various circumstances.
