173. Fatty Acids and the Olfactory Sense O F Dogs

No. 10] 753

173. Fatty Acids and the Olfactory Sense of Dogs

By Tohru UCHIDA ZoologicalInstitute, Faculty of Science, HokkaidoUniversity, Sapporo, Japan (Comm. by H. OHSHIMA,M.J.A., Dec. 1.3, 1956)

As long ago as the time of Homer's Odyssey, the dog was already known to have special capacity to distinguish the individual smell of different men. Because of this ability the dog is now employed as a police dog for trailing strangers. When suitably used, well-trained dogs can exactly follow the trails of those persons for some distance, despite the presence of several hindrances, such as attractive foods and disagreeable gaseous smells, on the way. While studying the olfactory sense of dogs, the writer, however, came across the fact, that butyric acid often arrests the trailing work of dogs. Butyric acid is specially used for assisting in the work training messenger dogs, because the smell of the fatty acids is very attractive to dogs. When the amount of butyric acid is too large, however, trailing dogs are often led astray by the smell; after having eagerly sniffed the smell, dogs generally urinate and abandon their work completely. On the other hand, it has been often observed by owners (or leaders) of dogs that their dogs while taking a walk turn upside down on the ground and rub their neck and shoulders against the ground for several minutes. The act is sometimes repeated two or three times. In doing so the fur of the neck and the shoulders generally becomes soiled by some glutinous substance which smells disagreeable to men. On closer examination of the spot on which the dogs rubbed their shoulders, one can often find the decayed corpse of some animal, such as that of a mammal, of a bird etc. It is generally known that decayed corpses of animals in putrification give rise to several kinds of fatty acids and their complexes, such as butyric acid, valerianic acid, caproic acid, caprylic acid, capric acid, etc. The smells of these acids are more or less similar to each other and rather disagreeable to the human olfactory organ. Inferring from these facts it was surmised that these fatty acids may have a remarkable influence on trailing dogs. Accordingly, the writer executed the following experiments. At first he selected about twenty Alsatian shepherd dogs, most of which had passed the examination for PD (police dog) in our country. These experiments were carried on in several localities from time to time, because the dogs and leaders suitable for, and willing to make, cooperation in the 754 T. UCHIDA [Vol. 32, experiments were not easy to get at once. Conditions of these dogs being variable from day to day, the dogs were subject to an examination to trail strangers from 300 m to 500 m prior to the experiment. The dogs, which did not succeed in that preliminary examination, were excluded from the following experiments. The dogs which passed the examination were, after 15 minutes, used for the trailing experiment, in which they were to follow a trail of 1,000 m made by a stranger. In the course of the trail were located a few marked spots whereon a fair amount of some fatty acid had been sprayed. These fatty-acid-complexes were made from putrefied bodies of earth-worms. When butyric acid was used, these dogs, though they sometimes eagerly sniffed the spots, succeeded in following their respective trail without difficulties. But, when the acids of still higher order were used, these dogs were found to follow the trail exactly to the marked spot and then they were all attracted by the smells, lost all interest and wholly abandoned their work. In these cases the acts of the dogs, though somewhat different in individuals, were in general as follows: they lifted their tail, licked the fluid of the fatty acids, turned on their backs, rubbed their shoulders on the ground and sometimes urinated. Of course, some of these acts were omitted by some dogs. It was observed that the female dogs urinated more often than the male, whereas the male generally lifted the tail and more often turned on his back than the female. After turning upside down or having urinated, they generally abandoned their work completely. The experiments were repeated on over a dozen dogs. Results are tabulated as follows.

Table I

As shown in the table above, when first tested with the fatty acids of higher order, the dogs always failed to retain th eir trailing No. 10] Fatty Acids and the Olfactory Sense of Dogs 755

ability in the first experiment. However, when the experiments were repeated several times, the dogs gradually became successful in trailing, although the acts, such as lifting the tail, licking the fluid, turning upside down, and urinating still took place. It must also be noted that the nomad dogs too turned upside down when they came across the spots treated with these fatty acids. Other experiments were carried out in winter. In the cities of Hokkaido, North Japan, the earth is covered with snow from the beginning of December to the end of March. The fresh sheet of snow presents especially a suitable condition for trailing experiments, because trails are not only easily observable, but also are scarcely affected by other smells on account of the fresh snow. Besides, the trails thus formed are always moist; which quality makes it easy for dogs to scent. Most's trailing cross was used as the trail for this series of experiments. From two opposite points, A and D, two strangers to the dogs, each wearing similar rubber boots proceeded walking synchronously toward the point 0. When the two strangers, A and D, met at point 0, they turned each to the right, thus forming a cross-trail. Therefore, AOD forms a straight line, and the distances AO and DO are equally 100 m long. The dogs used in this experiment all easily succeeded in following the trail AOB. A on the cross was always the starting-point. It was expected that the dogs would follow the trail AOB. The trail DOC was formed as a maze. After that the next experiment was executed. In this experiment the soles of the man A's boots were smeared at the start with some fatty acids. Stranger A, who followed the line AO, changed his boots at point 0 for new clean boots which were free from fatty acid. Thus, the trails were divided at point 0 into three kinds having different smell-complexes: AO retained the individual smell of stranger A plus the fatty acid, OB only the individual smell of A and DOC the individual smell of D plus the fatty acid. When a trailing dog starts at A and proceeds to the point 0, the dog must choose one of the courses, OC, OD, or OB. The trails OC and OD are similar in smell but only OB retains the individual smell of A and does not bear that of the fatty acid. The results obtained in these experiments were very different depending on the kinds of fatty acids here used, the ability of the dogs, and the persons by whom the trails were made. To train the dogs for trailing-work, they are generally trained at first to follow 756 T. UCHIDA [Vol. 32, the leader's (master's) trail, and, after they have been well trained, they are further taught to follow the stranger's trails; the police dogs are thus educated. Therefore, trailing their own lend€r is far easier for the dogs than trailing strangers. In Table II a~i g v en the results of experiments in which only the leader's or owner's trail was used. As is shown in Table II, two of the dogs which had not been well trained were easily attracted by the smell of butyric acid and abandoned their work completely (Nos. 16 and 17), whereas those suitably trained succeeded in doing what was expected of them in following trail AOB (Nos. 11-15).

Table II. Experiments on Most's trailing cross (butyric acid used)

Another series of experiments is described in Table III. In these experiments all the dogs were credited with PD. They pursued stranger's trails successfully, in spite of the presence of butyric acid.

Table III

Table IV illustrates the results obtained from the experiments in which fatty acids of order higher than butyric acid were used. In these experiments none of the police dogs could succeed in the assignment even when owner's (leader's) trails (Nos. 31-36) were used. No. 10] Fatty Acids and the Olfactory Sense of Dogs 757

Table IV. Experiments on Most's trailing cross (Fatty acids of higher order than butyric or their complexes used)

From the tables above given the following conclusions can be drawn. 1) Dogs not well trained to follow the trail of the owner were often distracted completely from their work by the smell of butyric acid. 2) When butyric acid was used and trail AOB was formed by persons very familiar to the dogs, they generally pursued the individual smell of A. The licensed police dogs succeeded in trailing strangers in the presence of butyric acid. 3) When the fatty acids of order higher than butyric and their complexes, such as caproic, caprylic, or capric acids were used, even the trail AOB formed by the owners or leaders was not traced by the dogs, which followed the scent of these fatty acids. Even those dogs well trained to stranger's trails preferred these fatty acids. The results can be summarized in the following formulae. Dogs well trained to follow the smell of strangers prefer the smells as follows: butyric acid (C4H802)< smells of strangers < smells or owners or leaders < caproic (C6H1202), caprylic (C8H1602), or capric acid (C10H2O02).

References Buytendijk, F. J. J.,: L'odrat du chien, Arch. Niederland. Physiol., 5, 434-457 (1.921.). Heitzenroder, C.,: Ueber das Verhaltenn des Hundes gegen einigen Riechstoffe, Zeits. BioL, 62, 401-507 (1.91.3). Henning, H.,: Geruchsversuche am Hund, Zeits. Biol., 70, 1.-8 (1920); Der Geruch, Leipzig (1924). 758 T. UCHIDA [Vo]. 32,

Kalischer, 0.,: Weitere Mitteilung fiber die Ergebnisse der Dressur als physiologischer Untersuchungsmethode auf den Gebieten des Gehor-, Geruchs- and Farbensinnes, Arch. Anat. Physiol., Leipzig. Physiol. Abt., 303-322 (1909). L'ohner, L.,: Untersuchungen fiber die geruchsphysiologische Leistungsf ahigkeit von Polizeihunden, Pfliiger's Arch. f. ges. Physiol., 272, 84-94 (1924). Most, K., and BrUckner, G. H.,: Ueber Voraussetzungen and den derzeitigen Stand der Nasenleistungen von Hunden, Zeits. f. Hundeforsch., 1, 9-30 (1936). Neuhaus, W.,: Ueber die Riechscharf e des Hundes f fir Fettsauren, Zeits. vergl. Zool., 35, 527-552 (1953). Niemand, H. C.,: 1st der Individualgeruch fur den Hund richtunggebend zum Er- kennen seines Herrn? Zeits. f. Hundeforsch., 12, 1-61 (1938). Schmid, B.,: Zur Psychologie der Caniden, Wolf-Hund-Fuchs, Kleintier u. Pelztier, 12, 1-77, Taf. 1-11 (1936). Seffrin, L.,: Ueber die kleinsten noch wahrnehmbaren Geruchsmengen einiger Riech- stoffe beim Hunde, Zeits. Biol., 65, 493-512 (1915).