In man, the nose or the sense of smell is the least acute of the five senses. Dogs have not as good sight as humans but in smell and sound excel them. The nose of the dog is a quivering, sensitive, active part of his body.
The dog is mostly nose and ear, for the sight of dogs is not as keen as that of humans, although dogs are quicker to discern moving objects.
Deaf dogs may be good watch dogs due to notice of intruders thur the senses of smell and vibration. A dog hunts a lost ball with which he has been playing, not so much by his eye as by his nose, and locates a moving noise by ear or by sound vibrations thur his body rather than by eye.
Sometimes on the street my dog rushes back and forth hunting for me. He does not look about him; he does not use his eyes; he smells at every passing leg, and sniffing at mine and without looking up, wags his tail and goes on about his play.
House dogs lose some of the keeness of scent but most outdoor dogs have a full, eager scenting sense. A pointer or setter, sniffing the game, knows by his nose whether it is live or dead. A good foxhound distinguishes between foot and body scents and thus can tell whether the game he is pursuing is fresh or tired, running straight or stumbling.
Most dogs hunt by scent. The coursing hounds such as greyhound, afghan, saluki, wolfhound and the like hunt chiefly by sight, not so much because they do not have scenting ability as because their speed enables them to keep the game in sight.
The bloodhound long has had the reputation of being the chief of scent trailers. German shepherds, airedaIes, great danes and doherman pinschers also can be trained to trail humans. Setters and pointers are scenters catching the scent in air or on grass and brush rather than from foot contacts on the ground. The beagles and foxhounds are foot or trail scenters. Most spaniels combine both aItho inclining toward body scent.
Bloodhounds follow the trail with nose close to ground; shepherds, commonly called police dogs, trail with the head about six inches from the ground and bark seldom on the trail. The dog taught to trail with nose somewhat above the ground has the advantage when the trail is broken, for he can pick it up more easily on the other side of the road or at some distance, such as on the other side of the stream. He depends more upon sniffing the air (body scent) than sniffing the exact trail spot (foot scent).
Scent is on the ground from the foot impression or hovering in the air just above the ground from the body. Bird dogs (setters and pointers) hunt almost entirely by air or body scent. This permits a faster running than does foot or ground scent.
What is an animal’s trail? The exceedingly small particles of smallbearing matter that come constantly from every living animal. The ordinary person can not detect them; blind persons, who develop the sense of smell, can at times distinguish and identify persons by their odors, just as does the dog.
Any part of the naked human body applied to a glass slide reveals under the microscope that it has deposited an oily liquid. This is true even after the skin has been thoroly washed. It is also true no matter how often the part of the body is applied to the glass slide.
This may be termed scent oil. It is present also in the feet of all animals.
But the strength of this scent as washed into the air in many small particles varies greatly even tho the same person or animal makes the scent repeatedly.
This is due entirely to the conditions of the atmosphere, to the direction of the wind, and to what might be termed, the breathing of the earth, for at times light movements of air rise out of the ground while at other times, it would seem that air is drawn into the ground. Naturally when the earth breathes out, so to speak, scent may be breast high and the dog can detect it readily, whereas at other times nose must be held close to the ground.
On a dry breezy day these smell-bearing particles from the animal body are short-lived and do not remain on the spot long. A strong wind is unfavorable also as it drives away or deadens these smell-bearing particles.
Damp (not wet) earth, protected by bushes and dead leaves, is good holding ground for the particles. City streets, especially where automobiles are crossing, are not favorable.
Tracks laid in cloudy weather lend themselves well to trailing, especially if the weather remains cloudy. The hot sun on tracks is unfavorable but if a mist later covers the ground, trailing may be successful.
New shoes leave little or no scent; they must be worn about two days before the footstep deposits a scent on the ground.
Scenting is not hindered by snow and ice. Thawing ground is more favorable than freezing ground. Dry cold air and freezing temperature either kill scent or do not hold it long. Soft wet snow and thawing ice are favorable for the trailing dog. Where the weather is extremely cold, the moisture may freeze the dog’s nose into ice and thus stop his work. A recently burned-over area is poor trailing surface but damp weather improves it. The use of rubber shoes for lessening scent avails little.
A trail older than six hours is a cold trail and few dogs can follow it. If the trail has been crossed by other animals or by other men, only the best work by the dog will keep him on the trail unless he can pick it up farther on.
A piece of clothing, some article handled much by the man sought, a spot which he has tramped considerably, are the means for giving the scent.
Scenting by dogs in the field working on birds is hard to judge at times. We believe that often the failure of a bird dog to locate game is not due to his scenting ability but to the contamination of the area and the air by the hunters and the horses they ride.
Human scent to the dog is strong and at times when a trail is laid by a man leading the game, for instance, a raccoon for a coon-hound trail, the dog will follow the raccoon’s scent in a parallel line, that is, he will follow the man’s rather than the raccoon’s scent.
Because the sand absorbs moisture quickly and retains it poorly, dogs can run over dry sand only by body scent and only a fresh scent. Clay soil, which holds the water near the surface and remains damp for days, will also hold a scent for a long time as will sandy soil.
Scent clings much to grass or leaves against which the body of the passing animal has contacted. For this reason a newly plowed field without vegetation is bothersome to the trailing dog.
Does the scent vary for different parts of the foot? There is a toe scent and a heel scent. Perhaps it is best to say that the scent is strongest from the ball of the foot. The toes touch the ground lightly and leave the light scent; then the ball of the foot being larger and laid down with more pressure, carries the heavier scent and because of this, the dog knows in which direction the animal or person has moved.