The Dog’s Nose (3)
by Dr. Resi Gerritsen and Ruud Haak
Odorants
According to Prof. Dr. J. Bodingbauer, we understand with smell ‘subjectively’ the ability, with the support of the nose used to sense smell, to pick up odor substances.
The sense of smell counts, just like the sense of taste, to the chemical senses. This is because adequate prickles are of a chemical character, with which these substances, in liquid or gas form, exert their influence on the sense. The supposition that the sense of smell could only be prickled by gaseous substances was convincingly countered by the experiment of Matthes. He proved that the lab animals he used (salamanders) could perceive in air as well as in water the odors of food. With smelling, odor substances are first picked up in a gaseous condition and than mixed with the thin liquid soil (mucous film) that covers the olfactory epithelium.
With smell, one can ‘objectively’ understand the characteristics of many substances to stimulate scent perceptions.
All living creatures give off odorants by their metabolism, breathing, glandular secretions, etc., by which every living being acquires his own (individual) odor. These odorants can periodically be of a different strength and composition. Dogs can observe organic connections in human sweat diluted a million-fold.
‘On moistened sand, dogs can work out a track about six hours old and on overgrown, moistened soil up to 24 hours,’ Scheunert and Trautmann said in their book. And they add to that: ‘Even if the track is washed put by heavy rainfall and after intensive radiation from the sun, scent perception is still succesful up to 3 hours after.’
Sniffing
The sniffing of dogs consists of a series of eight to twenty short puffs of inspiration followed by one expiration. During a single puff of inspiration, no whirls are formed in the nasal cavity, as was thought in the past. Prof. Dr. W. Neuhaus (1981) said the space between the turbinates is too small. The small amount and low speed of the air sucked in stays under the critical value for current turbulence. The inhaled air reaches the rear parts of the olfactory mucous membrane in the sinuses by differences in pressure in the nose.
Due to the considerable negative pressure from behind of the conchae maxillaris during inspiration, air is drawn from the spaces between the conchae ethmoidalis and from the frontal sinuses. At the end of the inspiration, scented air flows back into these spaces, so that even the parts of the olfactory epithelium located in the frontal sinuses and remote from the breathing flow are stimulated. During a single sniff, diffusion is of additional importance.
During normal breathing the pressure difference between inspiration and expiration in the rear space of the nose is too low to transport odor molecules to the remote part of the olfactory mucosa. However, molecules diffuse effectively into the frontal sinus if high odor concentrations and a minimal inspiration time of two seconds are maintained.
Breathed air comes in via the nostrils into the nasal cavity and is warmed and moistened then by the conchae maxillaris. After that the air stream will go along the conchae ethmoidalis and there be scanned by a lot of olfactory cells. After that, this air can come, as described earlier, through openings in the upper side of the nasal cavity into the sinuses and can make contact there with the olfactory epithelium.
(to be continued)
Figure:
Air current in the dog’s nose.
An air current moving through the dog’s nose, represented by the line beginning in the nostrils. Negative pressure comes into play behind the conchae maxillaris (M).
However, the air flow from the sinuses and the conchae ethmoidalis (represented by the arrowed lines coming down from the upper right) eliminates the differences in pressure.
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From: Dr. Resi Gerritsen and Ruud Haak, K9 Scent Training, A Manual for Training Your Identification, Tracking and Detection Dog.
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Bodingbauer, J. (1977). Das Wunder der Hundenase. Unsere Hunde, Vienna.
Scheunert, A. and Trautmann, A. (1976). Lehrbuch der Veterinärphysiologie. Verlag Paul Parey, Berlin.
Neuhaus, W. (1981). Die Bedeutung des Schnüffelns für das Riechen des Hundes. Zeitung für Säugetierkunde. Bd. 46, 301-310.
