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11/16/1999
Olfaction
A couple weeks ago, we discussed bubbles. I mentioned two
different views concerning the local temperature inside a
collapsing bubble subject to intense sound waves. Now I see that
the October 25th Chemical & Engineering News (C&EN) reports
a paper in Nature by some Russian workers who have actually
measured the local temperature in some bubbles and find it to be
in the range of about 2,000 to 5,000 degrees Centigrade. This is
in line with the work at Johns Hopkins that I mentioned and the
temperatures are far too low to promote nuclear fusion.
Actually, that idea did seem a bit far out, almost in the realm of
the discredited "cold fusion". Common sense appears to have
prevailed.
Speaking of sense, the sense of smell is often relegated to a much
lower level of importance compared with the senses of sight,
hearing or even touch. It is well known that the sense of smell is
key to our overall sense of taste and that when we have a bad
cold food loses much of its appeal. The October 22nd issue of
Science features articles on smell or, to be more sophisticated,
olfaction, while the above issue of C&EN also has an interesting
article on perfumes and their chemistry. Both sources contain
some surprising information.
For example, for centuries man has wondered how birds manage
to navigate thousands of miles and return to the same spot to nest
year after year. The same is true of salmon and turtles that return
to lay their eggs in the same spots where they were born. All
sorts of experiments have been done relating the navigational
talents to magnetic fields, positions of the sun, polarization of the
light, etc. Olfaction was relegated to a back burner and the
prevailing opinion was that birds don''t sniff around much.
Apparently, this feeling originated with various naturalists
including none other than Audubon, of the famed bird paintings.
He performed an experiment in the 1800s where he showed that
black vultures, presented with covered and uncovered carcasses,
much preferred to dine on the readily seen uncovered menu
selections. Having eyes, as well as a nose, I think I too would
have dived right into the visible tasty treat, were I a carrion
devotee!
This non-sniffing view began to change in the 1960s and 70s.
Betsy Bang, of Woods Hole, studied the size of the "olfactory
bulb" as a fraction of the brain size in various kinds of birds. She
found that this sensing organ comprised only 3 percent of the
brain in certain small songbirds. However, in some seabirds the
bulb was over 35 percent of the brain. At about the same time, an
ornithologist in Los Angeles found that turkey vultures were so
sensitive to the odor of their carrion repast that some engineers
employed circling vultures to lead them to leaks in gas lines.
Presumably, the vultures are attracted to the additive ethyl
mercaptan, an odiferous chemical that the vultures associate with
deceased animals.
Progress continued with the finding that pigeons could smell,
their olfactory bulb size lying intermediate between the songbirds
and the seabirds. Homing pigeons, of course, are a natural
subject for study. Within the last ten years, it was shown that
pigeons with wax plugged in their noses, or their sense of smell
deadened by an anaesthetic, took longer to find their way home or
weren''t able to get home at all. It seems as though they combine
their senses of sight and smell, with sight coming into play more
in their home territory.
I''ve developed more respect for birds recently, and not just
because they have now been shown definitely to have evolved
from feathered dinosaurs. We often deride someone as being a
"birdbrain". But the birdbrain is more complex than you might
think, especially in relation to mating. Consider the region in the
male canary''s brain that help it to warble so beautifully in order to
attract a mate. After mating season is over, this song center in
the brain shrinks, its primary task accomplished. An olfactory
equivalent is found in European starlings. This bird uses its sense
of smell to identify the proper green plants to select as materials
for building their nests. When nesting season is over, the starling
olfactory bulb atrophies, just like the canary''s song center. Why
waste good cranial real estate on unnecessary functions?
Now for the fish. Today there is great concern over the falling
stocks of salmon in the Pacific Northwest and consideration is
even being given to removing completely, or at least modifying,
certain dams along the Columbia River. Drastic measures indeed
to remove obstacles to salmon swimming upstream to spawn.
The role of olfaction in the salmon''s drive to return to their native
habitat has only recently been demonstrated. The key work also
came in the mid 70s when it was found that salmon were
imprinted with odors in their youth prior to heading out to sea.
This was demonstrated when a University of Wisconsin graduate
student raised some tagged coho salmon exposed to either
chemical A or chemical B. The fish were then released in Lake
Michigan. Two years later two streams were doped with the two
different chemicals. Some 90% of the fish that returned, right on
schedule, were found in the streams containing either A or B,
whichever the fish had been imprinted with in their youth. More
recent work has revealed the prime time(s) for imprinting as being
the time of increasing amounts of certain thyroid hormones.
There''s another type of "homing" associated with odors. This is
the attraction of mating prospects in the animal or insect world
through the employment of odiferous "pheromones". These
powerful attractants can sometimes exert their effects over
surprisingly long distances in certain species. There has been
some controversy over whether or not the pheromone effect
occurs in humans. That is, do you fall for someone based partly
on his or her odor? The perfume industry has certainly gone all
out to try to convince us that this or that concoction will convince
the opposite sex to pursue various social interactions with you.
But what are the facts? One recent attempt to check such claims
scientifically involved a University of Chicago study of the effects
of a male steroid androstadienone and a female steroid
estratetraene, claimed to attract females and males, respectively.
These two substances were incorporated in solutions in clove oil
and then either the steroid solution or pure clove oil scents were
swabbed under the noses of two groups, each group consisting of
ten young men or ten young women. During the experiment,
some sort of standard psychological mood tests were run on the
subjects. Surprisingly, the women proved to be "happy and
energized" after swabbing with either steroid while the men felt
"tired and less elated" after being subjected to the same steroids!
To be honest, I''m a bit confused as to whether the man or the
woman should wear the steroid-containing scent for optimal
results. So far, the conclusion seems to be that these particular
steroids may serve to modulate behavior but, unlike the
pheromones, do not predict the eventual path of the male-female
relationship. Perhaps this is just as well! Both men and women
can feel secure in the knowledge that they''re still in control of
their own sexual destinies. On the other hand, the seducer may be
disappointed that that expensive fragrance does not guarantee a
receptive seducee. Note that the subjects of the study were
"young", obviously making the results of dubious significance for
those of us who are senior citizens and whose olfactory
equipment is considrably degraded.
Indeed, one hears these days more and more about individuals
who are positively repelled by fragrances. This aversion to
fragrances falls under the general category of multiple chemical
sensitivity (MCS), a quite controversial form of allergy. I recall
several features on "60 Minutes" or "20/20" in which certain
people were apparently so sensitive to chemicals that they were
virtual prisoners in their sanitized homes. Venturing outside for
these victims of MCS results in them becoming quite ill with
various symptoms such as migraine headaches, shortness of
breath, or other distressing maladies. Various experts on both
sides of the question were interviewed, saying either that the
effect was real or that it was all in the victim''s heads. Indeed the
term "nocebo" was coined, the nocebo being the opposite of the
placebo. You feel bad if you think the material is bad for you.
Skeptics point to research in which, when the odor of an
offending substance is masked, the subjects do not become ill,
suggesting a nocebo effect when they smell that substance.
The situation in Halifax, Nova Scotia, is perhaps an extreme case
of fragrance aversion. There are no-scent signs in public places
and fragrance-free sections in churches. In their Dalhousie Arts
Center, management will try to move concert patrons to seat
locations away from those who are felt to be overly scented.
Here in the U.S., the FDA is presumably protecting us from any
dire consequences of dangerous constituents in our fragrant
products. Health Canada, the governmental counterpart of the
FDA in Canada, has not found any specific agent that causes
MCS. Indeed, the legality of banning scents, as in Halifax, is
under scrutiny. An impressive-sounding organization in Canada,
the Scented Products Education and Information Association of
Canada (SPEIAC), has recommended that people wearing scents
should only use enough to be detected within an arm''s length of
the wearer. I suggest that this may not be a practical rule to carry
out in practice in that it implies a cocoon of odor traveling with
the scented one. No provision is made for the lingering odiferous
molecules trailing behind a fast moving individual, or even a
slowly moving temptress in a cocktail party situation.
Well, the perfumer has enough of a challenge as it is. According
to the C&EN article, there are about 3,000 different ingredients
that are available to be combined to form a perfume. And it
appears as though the human response to odor is quite definitive.
Either you like an odor or you dislike it. There doesn''t seem to
be an in-between reaction. I''ve been sitting here trying to think of
odors I can take or leave but haven''t come up with one. Just
yesterday, I inadvertently drove over a bit of the remains of a
skunk and the odor brought forcefully to mind one of the few
things I remember from organic chemistry. If I remember
correctly, the odiferous skunkish compound is beta-methyl indole,
also known as skatole. Surprisingly, indole is one of the
components used, and not so sparingly, in creating the scent of
jasmine, a scent said to be employed in over 80 percent of
women''s and about a third of men''s fragrances. The C&EN
article quotes the author Susan Irvine as attributing the attraction
of the jasmine fragrance to "the way the rich flux of its perfume is
undercut with a carnal taint of flesh, due to its high percentage of
indole". Indeed, this is racy stuff!
Another surprising ingredient used by perfumers is ambergris. I
looked up the word in my Webster''s New World Dictionary and
found that ambergris is "a grayish, waxy substance from the
intestinal canal of sperm whales, often found floating in tropical
seas". I was spurred to look up the word by the C&EN''s article
calling ambergris "a kind of whale vomit"!
I hope I haven''t turned you off completely but rather have shared
with you just a few of the wonders of olfaction. I will continue to
smell the roses on my walks, which often take me past a small
rose garden dedicated by the homeowner to the veterans of past
wars. I am finishing this column on Veteran''s Day and would like
to say my personal thanks to Bill Guyer and "Shinney" Fetrow.
Bill, our neighbor in Mechanicsburg, Pennsylvania, was lost in the
skies over Burma in World War II. Shinney was a high school
classmate who became a paraplegic, wounded in Normandy on D-
Day. His cheerfulness and uncomplaining acceptance of his fate
was an inspiration to us all.
Allen F. Bortrum
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