Tears: 2 of 2

J. Moore (j#d#.moore@canrem.com)
Sat, 21 Oct 95 22:34:00 -0500

Tears: 2 of 2

This second part of my post deals with tears and what they contain,
and what this means in regard to the likelihood of tears being an
excretion system.

When Morgan cites William Frey's work as support for the AAT; her
reasoning is twofold:

1) She claims that emotional tears are shed by humans, aquatic
animals, and Indian elephants, and by no other animals. Part one
of my post showed that the evidence for this does not exist.
There are no documented cases of emotional tears being shed by any
nonhuman animal, and though there are anecdotal reports of such
tears in nonhuman animals, these report such tears in many
non-aquatic animals. So it cannot be said to be a trait shared
only by humans, aquatic animals, and Indian elephants.

2) Frey's work demonstrates that emotional tears do serve an
excretory function, and Morgan claims that the original function
of emotional tears was the elimination of salt.

First we have an interesting point; then we have to clear up
some confusion introduced by Morgan's inaccurate terminology.

The point is that the composition of tears does show an excretory
function of tears which sheds light on their environment of
origin. This feature of tears, that they are excretory in
regard to some elements, was known even before Frey's work.
The actual composition of tears, as opposed to some imagined or
postulated composition, is not favorable to the AAT, but we'll
come to that at the end.

The problem is the confusion Morgan has introduced regarding
the types of tears. She uses the term "psychic tears", and
posits these as being one of two types of tears, the other being
"reflex". She claims there is "general agreement on this", but
in fact she is confused. The two types of tears are "basic" (now
generally called "basal" or "continuous" tears) and "reflex" tears,
and there is in fact general agreement on this. Emotional,
also called "psychogenic", tears are one form of reflex tears.
The stimulus is emotional rather than being irritant-induced.
Basal tears are the normal tear contribution to the "tear film"
which lubricates the eye.

"Reflex secretion may be of *peripheral sensory origin* through
fifth nerve stimulation (cornea, conjunctiva, skin, nose) or of
*central sensory origin*. In the latter the stimulation may be
retinal, varying with the intensity of light, or psychogenic, as
in weeping caused by emotional disturbances or by various central
nervous system diseases. The production of tears on an emotional
basis is unique to humans among all vertebrates".
(Benjamin Milder 1987:24)

************ The excretory abilities of the lacrimal glands ***********

As has been pointed out in this newsgroup, to be involved in
changing the body's balance of a substance, such as salt (the
balance in what we are talking about is the balance of water
to a given substance), any given excretion must contain a
concentration of the substance that is greater than its
concentration in plasma, which is called being "hypertonic".
An organ which does this is said to be capable of "active" rather
than "passive" excretion for that substance. That the lacrimal
glands can and do perform active excretion is well known to those
in the field of ophthalmology. However, they are not capable of
actively excreting sodium, as the AAT requires.

Central to Morgan's thesis is that our lacrimal glands actively
excreted salt at some time in the past, even though they don't
now. This requires that our lacrimal glands underwent two massive
changes, starting and ending with a passive secretion of sodium.
This idea is certainly far less parsimonious than the idea that
the observed and measured active secretion of the lacrimal gland
indicates our actual environmental past habitat.

***************** Secretions in tears ********************************

The facts on substances which the lacrimal gland is capable of
actively excreting, and on sodium, which the lacrimal gland cannot
concentrate sufficiently for active excretion.

"Sodium in tears is about equal to that in plasma and has been
found to correlate with it, suggesting a passive secretion into
the tears.
"Potassium, with an average value of about 20 mmol/l is much
higher than the corresponding plasma concentration of about 5
mmol/l. This indicates an active secretion into the tears".
(van Haeringen 1981:92)

"The manganese concentration of emotional tears (25.2 +/- 6.6 ng/ml)
was not significantly different from that of irritant-induced
tears (34.2 +/- 8.8 ng/ml) obtained from the same healthy female
subjects". (Frey et al. 1981:564)

"The manganese concentration of emotional tears from women exceeded
that of serum (0.98 +/- 0.09 ng/ml) obtained from the same
subjects by about 30-fold". (Frey et al. 1981:564)

"Paired samples from 25 women also showed that the protein
concentration of emotional tears was 24% greater than that of
irritant-induced tears (P<.01) (Table 1). We found a higher
protein concentration for emotional tears from men as well
(P>.05), although we obtained paired samples from only four
subjects". (Frey et al. 1981:562)

The only higher concentrations that Frey and his colleagues found
being excreted in emotional tears as contrasted to
irritant-induced tears were higher concentrations of proteins.
Frey feels that the process of crying helps in emotional release
through eliminating substances such as prolactin, ACTH,
Leucine-Enkephalin, and manganese. He also feels that the levels
of prolactin in one's system provide a threshold effect, affecting
how easily emotional tears are shed in response to a given
stimulus. This, he thinks, accounts for his findings that
women "shed tears more often and more readily than men". Adult
women typically have much higher levels of prolactin than adult
males, and these levels also rise during pregnancy, another period
when emotional tears are known to be more easily shed.

************ Innervation of tear secretion ***************************

Morgan has suggested that the source of control for psychogenic
tearing is important to her theory, but this is based on her
mistaken idea that human emotional tearing is a characteristic
shared by aquatic animals and no other animals. This has been
shown to be a completely unsupported notion: there is no
documented evidence for nonhuman aquatic animals shedding
emotional tears, and the anecdotal and non-documented evidence
is at least as strong or stronger for emotional tears in
non-aquatic nonhuman animals.

What matters is the ability of lacrimal glands to excrete
hypertonic substances. If they cannot excrete a given substance
with a greater concentration than it appears in plasma
(i.e., "hypertonic"), the purpose for these tears cannot be
for excretion of an excess of that substance. It is
well-documented that human tears are never hypertonic in
regard to sodium.

Tears are, however, strongly hypertonic in regard to potassium.
In this regard, the lacrimal glands call to mind the "salt"
glands of terrestrial reptiles and birds. Morgan has many times
inaccurately claimed that salt glands are only found in marine
birds and reptiles, ignoring the many terrestrial birds and
reptiles who have these glands. These animals include ostriches
and other birds, and lizards, including iguanas, chuckwallas,
and others. The "salt" glands of these terrestrial birds and
reptiles, unlike those found in marine birds and reptiles, are
used primarily to excrete potassium. "In other words the
secretion resembles that of the ostrich and differs markedly in
composition from that of marine birds and reptiles" (Peaker and
Linzell 1975:247-8).

So the actual observed and measured excretions in human tears
far more closely resemble the excretions from the "salt" glands of
terrestrial birds and reptiles than those of marine birds and
reptiles. Thus for human tears' excretory abilities to indicate a
terrestrial background requires no change. For their abilities to
indicate a marine background requires not just one but two massive
changes, starting and ending with a passive secretion of sodium.

This idea is certainly far less parsimonious than the idea that
the observed and measured active secretion of the lacrimal gland
indicates our actual environmental past habitat, which evidence
from tears suggests would be terrestrial rather than aquatic.

********************** References **************************************

1975 *Salt Glands in Birds and Reptiles* by M. Peaker and
J.L. Linzell (Dept. of Physiology, Agricultural Research Council,
Institute of Animal Physiology, Babraham, Cambridge). Monographs
of the Physiological Society No. 32.
Cambridge University Press: Cambridge, London, New York, Melbourne.

1981 "Clinical Biochemistry of Tears" by N.J. van Haeringen, Ph.D.
*Survey of Ophthalmology* 26(2):84-96.

1981 "Effect of stimulus on the chemical composition of human
tears" by William H. Frey II, Ph.D., Denise DeSota-Johnson, B.A.,
and Carrie Hoffman, B.S.; and John T. McCall, Ph.D.
*American Journal of Opthalomology* 92:559-567.

1985 *Crying: The Mystery of Tears* by William H. Frey II, Ph.D.
with Muriel Langseth. Minneapolis: Winston Press.

1987 "Chapter 2: The lacrimal apparatus" by Benjamin Milder, M.D.
In *Adler's Physiology of the Eye: Clinical Application*,
edited by Robert A. Moses, M.D. and William M. Hart, Jr., M.D., Ph.D.
Eighth edition. The C.V. Mosby Company: St. Louis, Washington, D.C.,
and Toronto.

Jim Moore (j#d#.moore@canrem.com)

"I agree with Montagu's view that 'the shedding of tears as an
accompaniment to emotional distress has been attributed to other
animals... The truth, however, appears to be that while some of
these animals may on occasion exhibit the evidences of tears,
this occurs very seldom, and is the exception rather than the
rule. ...Psychic weeping is not known to occur as a normal
function in any animal other than man.'" William H. Frey (1985:147)

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