Part 2: What is Scent?

Tuesday, August 01, 2017 12:30 AM | Front & Finish (Administrator)

Written by Michael Pumilia

Scent is those micro particles out there that can be smelled. How’s that for a simple explanation to what could be a complex answer? But for us to use as an easy way for everyone to understand, it is an elegant answer. A more correct, simple answer is also what I call the Molecule Theory of Scent. The things that we and most animals use to identify thousands of things living, dead, or inanimate objects are molecules – little capsules of atoms all put together. A molecule leaves its origin, floats in the air, and/or lands on the ground and is swept up into the nostrils of the receiving animal. Once there, the sensors in the nostrils tells the brain what was found and the brain checks its memory bank to identify the molecule. Either the molecule has been experienced previously or not. The next query the brain makes is to decide whether the molecule is interesting enough to follow or not. The second question is based on experience and/or expectation. For the dog that is tracking, it must decide if the scent is the target scent.  The training for tracking is to teach the dog what you want it to follow.

In the wild, animals find many scents each day. Their survival depends on their nose. For example, a fox runs across a particular scent. It identifies it as a rabbit. The next question is answered with, “Yes, I’m interested.”  But experience tells it whether to follow or not. A young fox might decide to follow, but the more experienced fox would be able to discern the age of the track. If it’s recent, then, “yes, I should follow.” But if it is old, then, “No, don’t follow.” This gets us to the next part of experience. The young fox would not know which way to go – left or right. The more experienced one, by sniffing both left and right, would be able to understand that the rabbit in this case went from right to left in figure 1. Likewise, if the fox starts out to the left in the figure and later runs across still another scent, it would again make its decisions. In this case, the cross track is a moose. The experienced fox disregards it and moves along.


Figure 1.

            The best example I’ve ever seen to explain the Molecule Theory of Scent was on an old black and white TV set back in the early 1970’s. The camera was focused on football player Otis Sistrunk of the Oakland Raiders sitting on the bench. The player was very warm although the weather was cold. Steam rose from his shaved head while sweat dripped from his chin. With the body’s heat rising, the sweat at the top of the head is carried aloft as steam. Sweat on the lower face forms at each pore and the sweat collects into droplets which gravity then makes them stream down and off the face. But steam and sweat are two forms of the same molecule. Throw in a few grains of salt with water and you make sweat. This is a matter of how many molecules are collected together, vapor versus liquid. The vapor carries along in the breeze much further than the liquid, just like clouds versus rain. The vapor is affected by the wind; the liquid by gravity.

            For a human, our scent is the combination of everything we are and wear. Our skin and hair follicle are always falling off, in addition to sweat. These intermingle with what we wear such as soaps, shampoos, colognes, greases, and food. Then you need to add in the things our clothes have been washed in, touched, or what has been carried in the pockets. All of this identifies what scent we scatter about as we pass through this world. Our dogs learn early on who we are by our scent. And also they learn what food is, especially human food, which seems to be much better than doggie foods. This probably explains why they can tell which pocket has the doggie treat real early in life. We probably have all seen the TV pictures of herds of seals on a shore and pups everywhere but the mother and child always know how to get back together with one another. It’s scent.

            Actual scent of people, dogs, and all other animals is a complex grouping of individual characteristic molecules that make each individual different and recognizable. If you had a group of 30 dogs of the same breed, each has a unique set of identifiers, a chemical signature. One part of the signature defines that the object is a living thing, another identifies it as a dog, another identifies it as a particular breed, then on to sex, age, etc. Plants have unique smells. Inanimate objects like rocks, dirt, fluids, solids and water all have a scent; it depends on what is mixed in with it.

            In tracking, we tend to focus on the human and ground cover scents. The person laying the track imparts both his smell to the ground and also by crushing the cover underneath his feet .This is known as the grass effect. Some people say dogs track the grass effect more than the person. It may be true with beginning dogs, but the human scent is quickly focused upon through training. The human scent is carried to the ground thus creating a path by three means. First, the heavier molecules fall to the ground by gravity. Second, the lighter particles are blown about by the wind. Third, even if the air is still, the movement of the person through the air creates turbulence. Each method changes how the overall scent finally gets to the ground and where.

Gravity makes the heavier scent molecules fall around our feet. By moving up hill and down hill, it causes gravity to spread the scents in certain ways. By stomping each foot as a person walks, a greater scent trail occurs as additional molecules are shed from the body.

 Next, so many people focus on tracking as two dimensional. They feel a track is only so many yards forward and perhaps cast left or right from the pathway.  It’s really a three dimensional world. The smell is also carried away by the breeze. At a distance it may fall again to earth. But it can be stuck on fence lines, bushes, buildings, and trees. In addition, scent molecules can flow through lines of objects and then come to the ground further away. The wind also creates swirls, voids, and pools of scent. A depression in the ground and even puddles of water can store a reservoir of scent molecules which has more scent than the track. 

 The movement of the tracklayer, while vigorously swinging the arms, causes scent to be scattered even further than you might think. It may not be a lot, but it does have a consequence.

The strength of the scent diminishes with time. One theory is that the airborne molecules dissipate in approximately 30 minutes. The gravity-borne molecules fade but this can be several days later. In these conditions, a good tracking dog can follow the trail. Many an escaped convict can vouch for that. And a lost child can be found.

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