2. Morgan cites Denton
J. Moore (j#d#.moore@canrem.com)
Tue, 5 Sep 95 17:55:00 -0500
*** Section 2: Morgan's and Denton's quotes ***********************
In this section I quote from Morgan's 1990 book to show that she
does in fact make these claims, and from Denton's 1982 book to
show that Morgan's claims are not supported by the very book she
cites, and quotes, in support of them:
1 ******
Morgan claims:
While other mammals have a innate physiological reaction to salt
need, humans have no such innate physiological reaction to salt
need.
Morgan, pg. 100:
"A salt crisis in our evolutionary history would go far to
explain one other specifically human characteristic -- the fact
that we have no instinctive awareness of the state of the sodium
balance in our bodies."
Morgan, pg. 102:
"An ape living on sea food would have been comparatively well
placed to adjust to a saline environment. <2 sentences about
sweating deleted> The instinct for responding to 'salt hunger'
could well have been lost at this stage."
Denton quote, pg. 605:
"The hedonic human liking or appetite for salt when it is available,
and independently of any metabolic need, is an evolutionary legacy
of high survival value. It is part of the overall innate
organization dedicated to salt ingestion along with the elements
determining appetite response to sodium deficiency and to the
hormones of the reproductive process."
Denton quote, pg. 605:
"Further, learning or habituation may be predominant in
the gradual augmentation of intake over years. Indeed, even in a
herbivorous creature such as the sheep, whose highly developed
appetite organization has been extensively investigated, it is
obvious that learning mechanisms become richly superimposed on
innately generated drives. This, of course, is characteristic of
innate mechanisms in that most can be modified by learning.
But in the human case, the cultural influences are acting in the
context of an innate propensity: the liking for the taste of salt
and readiness to ingest it."
2 ******
Morgan claims:
Humans do not undertake any compulsory search for salt when
deficient, and human intake of salt bears no relation to salt
deficit or surplus.
Morgan, pg. 101:
"In humans neither the compulsory search nor the abrupt cut-off
point can be relied on. Their intake bears no relation to salt
deficit or surplus."
Denton quote, pg. 117:
"A searching example of the 'set point' of sodium homeostasis has
been made by Hollenberg (1980). He emphasizes that sodium
homeostasis, especially control of extracellular volume, is an
excellent example of a feedback control system. The afferent and
efferent limbs of the system have received considerable attention
but the 'set point' has received remarkably little emphasis. He
notes a personal clinical observation of a normal man, in sodium
balance on a 10 mmol/day intake, inadvertently being given a 30
mmol sodium load intravenously and promptly excreting it."
Denton quote, pg. 117:
"Similar findings have been documented in several studies
(Braunwald et al. 1965; Hollenberg et al. 1972), including the
outstanding work of Strauss and colleagues (1958). They showed
that a person in balance on a low-salt diet responded with a
prompt natriuresis to a 30 mmol sodium load. If a diuretic was
administered beforehand and 100 mmol of sodium lost, then the 30
mmol load did not cause natriuresis. Indeed this did not occur
until the 100 mmol lost with the diuretic was replaced. The data
suggest the 'set point' around which sodium balance cycles in the
normal person is that amount of sodium chloride in the body when
the person is in balance on no-salt intake (Hollenberg 1980)."
Denton quote, pg. 180:
"Yensen (1959) showed that salt deprivation in two normal humans
reduced the taste threshold for salt to approximately 1 mmol/l,
but did not alter the threshold for sour, sweet or bitter
substances. No salt craving developed, but at meals the subjects
felt the food would taste better with salt. Forced drinking of
water, which resulted in negative sodium balance, lowered taste
threshold and this was not associated with lowered salivary Na/K
ratio (de Wardener and Herxheimer 1957). An intense craving for
salt developed in the subjects."
3 ******
Morgan claims:
Other mammals respond just as urgently to a deficiency in salt
as they do to a deficiency in water.
Morgan, pg. 100:
"When we are suffering from a deficiency of water we feel thirsty,
and take active measures to find a source of water and set the
balance right. If the thirst remains unslaked it intensifies until
all other considerations become subordinate to the need to drink.
Most mammals respond just as urgently to the need for salt if
they are deprived of it."
Denton quote, pg. 221:
"A characteristic feature of salt appetite is the delay in its
appearance despite large rapid loss of sodium. With sheep the
delay is usually 24 h, with rats 4-8 h. This is in striking
contrast to thirst."
Denton quote, pg. 223 (concerning sheep):
"The results of experiment (i) on five animals were clear-cut.
As Fig. 12-1 (results on four animals) shows, any significant
increase in voluntary drinking of sodium was delayed 2-4 days, by
which time there was severe deficit."
Denton quote, pp. 223-224 (concerning sheep):
"Whereas sodium intake was delayed, water intake usually rose on
the first or second day (Abraham et al. 1976)."
Denton quote, pg. 224 (concerning sheep):
"Overall, however, the data confirm the delayed onset of appetite
despite very rapid large loss of salt.
Other studies, with other methods, also indicate this delayed
onset. The contrast with thirst is striking."
Denton quote, pg. 458:
"The signal or outstanding feature of salt appetite, apart from its
being innate, is the time delay in its onset. It follows 4-72 h
after establishment of body deficit in the naive animal, be that
rat, sheep or rabbit."
Denton quote, pg. 458:
"The character of the behaviour contrasts with thirst. Though
the two ingestive behaviours have common elements in the operation
of taste factors and oropharyngeal metering of inflow associated
with satiation of appetite, the excitation of them is quite
different. With thirst a sudden rise in the [Na] (sodium
concentration) of cerebral arterial blood contrived by intracarotid
infusion, or a rise in angiotensin concentration produced
similarly, results in avid drinking within 30-120 s. Similarly
with isosmotic volume depletion contrived by sequestration with
formalin, polyethylene glycol or haemodialysis, the onset of
thirst is rapid. The reaction of the osmoreceptors, sodium
receptors, and possibly angiotensin II receptors as well as those
transmitting from the left atrium via the vagus is rapid, the
redirection of the stream of consciousness as a result of
reticular arousal and cortical reaction is rapid, and the seeking
and drinking of water is more or less immediate according to
circumstances."
4 ******
Morgan claims:
Other mammals take in the precise amount of salt they need to
correct their deficiency and then "will take no more".
Morgan, pg. 100:
"Derek Denton, in his classic study *The Hunger for Salt*,
describes his researches into salt appetite in non-human mammals
such as sheep, rats and rabbits. In all these species there is
a precise correlation between the amount of salt their bodies
need and the amount they will take in."
Morgan, pg. 101:
"On the other hand, when an animal has had enough salt it will take
no more."
Denton quote, pg. 221:
"In rats with sodium deficit as a result of adrenal insufficiency,
the characteristic behaviour was to overdrink considerably
relative to deficit."
Denton quote, pg. 549:
"Within a particular species, such as the sheep, there may be
large individual variation in the 'set' of the hedonic or
palatability mechanisms determining 'need-free' intake of salt.
Given the same environment and dietetic conditions from birth, and
these, for example, involving low but adequate salt intake in food
and water, some animals when given free access to sodium solutions
behave as salt gluttons, whereas others ingest little or no salt."
Denton quote, pp. 184-185:
"In relation to the characteristics of salt ingestion by rats on
a diet with adequate sodium content, Richter (1956) has represented
the parameters of the behaviour as shown in Fig. 10-13. A typical
set of observations is shown in Fig. 10-8. Similar types of
preference behaviour are shown towards other substances, for
example sucrose and alcohol. Clearly this does not reflect any
bodily deficit but a liking for the substance (Young 1948).
Young (1948) has pointed out that in terms of the theory that
intake indicates bodily need, one would expect the average daily
intake of a substance to be approximately constant under the same
set of intraorganic conditions. However, in the normal rat the
quantity of fluid ingested varies markedly with concentration.
Weiner and Stellar (1951) have also pointed out that the ingestion
of some constant amount of salt is not the goal of animals studied
in relation to salt preference. Their experimental technique also
revealed that the rats drink the preferred concentration much more
rapidly."
Denton quote, pg. 209:
"_Summary of sheep experiments_
These experiments had certain clear results.
1. In all animals development of sodium deficiency caused a
large voluntary intake of sodium solutions. Onset of the
appetite, whether indicated by clear change of behaviour or intake
of solution, was usually delayed 2-5 days.
2. Sodium intake was eventually adequate to maintain the animals
in good condition physiologically. There was variation, however,
in whether the sodium status was maintained on the positive side
with a sizeable amount of sodium in the urine, or whether near
neutral or slightly on the negative side."
Denton quote, pg. 211 (concerning sheep):
"However, despite the naive animal sometimes approximating intake
to the extent of its deficit from first instances of sodium
deficiency, it is obvious that with many animals a large element
of experience and learning antecedes such behaviour."
While we can see from the Denton quotes above that non-human
mammals do not generally have an "abrupt cut-off point" when it
comes to salt intake. Note that the rabbit is an exception to
this general rule:
Denton quote, pg. 240:
"_Rabbits_
The intriguing data on the capacity of adrenalectomized rabbits to
repair body deficit precisely without excess intake are dealt with
in Chapter 14 bearing upon satiation behaviour."
Denton quote, Chapter 14, pg. 255:
"Wild rabbits, sodium-deficient as a result of adrenal insufficiency,
take 9-12 h to correct deficit whether large or small. That is, the
rate of drinking is determined by the amount of deficit. The precise
correlation between deficit and intake is striking."
Denton quote, pg. 258:
"_Rabbits_
The results of studies by Dr J. Nelson on the time course of
satiation of sodium deficiency by wild rabbits have been rather
remarkable."
Denton quote, pp. 258-260 (concerning rabbits [pg. 259 is figures]):
"Fig. 14-4 shows the time course of correction of sodium deficit.
The deficit was exactly replaced by 12 h. The animals were still
in exact balance at 24 h, indicating there was no overshoot as
with rats. The striking feature was that the same linear
correlation between intake and initial deficit was seen at 2, 4, 6
and 9 h (Fig. 14-5) and the correlations at all times were highly
significant (P<0.01 at all stages). Whereas the animals were
slow to repair deficit, the rate of drinking was always related to
the degree of the initial deficit, the more deplete animals
drinking faster over the 12 h. If the animal were less deplete it
drank slower though the rate of drinking with large deficit showed
it could have repaired the small deficit in much less than 9-12 h.
Additional to the observation on no overshoot noted above, the
rabbits were also in balance at 48 h."
5 ******
Morgan claims:
Non-human mammals go to great lengths to satisfy their salt
hunger, but humans do not.
Morgan, pg. 100:
"Species living in habitats far from the sea go to great lengths
to satisfy their salt hunger."
Denton quote, pg. 89:
"There is an emphasis in relevant historical records on a human
preoccupation with salt. Sometimes this may amount to a craving
and people may endure great hardships and take risks to obtain
it."
Note: Morgan followed her above sentence with two paragraphs of
examples drawn from Denton's book, but somehow managed to misplace
his mentions of humans in them. She also seems to have entirely
skipped Denton's Chapter 5, "Salt in History: Symbolic, social and
physiological aspects". Just a coincidence?
Quotes marked "Morgan", unless otherwise noted, are from:
1990 *The Scars of Evolution* by Elaine Morgan. Souvenir Press: London.
Quotes marked "Denton" are from:
1982 *The Hunger for Salt* by Derek Denton. Springer-Verlag: Berlin,
Heidelberg, New York.
*******************************************************************
Jim Moore (j#d#.moore@canrem.com)
* Q-Blue 2.0 *
|