Re: Nostrils: a definition

David L Burkhead (r3dlb1@dax.cc.uakron.edu)
1 Aug 1995 01:28:40 GMT

In article <772871178wnr@desco.demon.co.uk> Elaine@desco.demon.co.uk writes:
>
>Comment from Burkhead: the trajectory of breathing isn't awkward
>, it doesn't matter whether the path is straight or curved.
>
>Negus spent a lifetime writing heavy tomes on the rsspiratory canal and
>do4sn't go with you
> Comparing " for instance a fat-running horse or deer to a considerably
>slower Man, he says "in the latter there is a tortouos airway withsharp
>angles at the anterior and posterior choanae and at the larynx. In
>addition to tortuosity there is obstruction at the internal ostium and
>at the glottis. There are eddies produced in Man, esp. in the gao
>between the posterior nasal passage and the laryngea aperture.."

This physical description says little to nothing about airflow
difficulties, which is what _you_ talked about in your previous post.
The air viscosity, flow rates, and Reynold's numbers for airflow
through the nasal passages are such that the difference in energy
expenditure between straight and curved is utterly trivial. Thus,
there is no particular advantage, one way or another from that aspect.

>
>"While the nose of many vertebrates has reached a high degree of
>perfection for humidification, for olfaction, or for rapid transfer of
>air currents, the organ in Man is a rather poor affair "

"Rapid transfer of air currents" is _not_ the same thing as flow
rate. It is current _speed_, which is important for cooling (both
convective and evaporative). Since many large vertebrates use the
airflow through their snout to cool cranial blood--allowing body
temperature to rise without cooking their brains--they would, of
course, want to maximize that. However, "many vertebrates" are not
the subject of this debate--aquatic animals and primates are.

Specifics, not vague generalities.

As for "olfaction"--humans don't rely heavily on smell.
Therefore, there would be no great incentive for maximizing that. And
its ability at "humidification" is entirely adequate to human needs in
even the driest of climates, so I fail to see what improvement would
need to be made there--and would be selected for.
>
>While looking this up,I cam across this nice little comment:
>
>In aquatic species the odorous molecules are perceived when in solution
>in water. In terrestrial species a smell conveyed in pure aqueous
>solution is not perceived. But if dissolved in saline solution, the
>odour may cause stimulation.
>
>"It is somewhat surprising that in terrestrial Man, salt is essential.
>Whether this phenomenon applies to terrestrial vertebrates other than
>Man does not appesr to be determined."

So why not wait until the _evidence_ is in before crowing about
it? BTW, when was the last time _you_ smelled something in salt
water.

This, if true, would actually contradict some of your own claimed
evidence--the downward pointing nose to "protect" the nasal passages.
An adaptation that relies on smelling scents in water iscontradictory
to keeping that water from reaching the scent receptors.

David L. Burkhead
r3dlb1@dax.cc.uakron.edu
d.burkhead@genie.geis.com
76435.1332@compuserve.com

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