FOOD AND FLAVOR
_The Biological Rôle of Taste_
IN considering the function of the sense of taste it is common to
dismiss the topic in a summary manner by pointing out the fact, that in
its original primitive conditions, at least, this sense enables the
organism to discriminate between wholesome and deleterious food. This
function is, of course, not to be neglected, especially if due credit be
given to the rôle played by smell in the same service. It is however
true that, although the indications of taste and smell may be, for lower
forms of animal life, fairly trustworthy guides in the selection of
edible substances, such criteria as taste and odor can by no means be
relied on by human beings. In a general way it is, of course, true that
wholesome substances possess taste qualities which are agreeable and
enjoyable, while foul, decaying and poisonous substances are often
characterized by tastes and odors that arouse in us disgust and
revulsion.
But in the complex lives of human beings, at least, this sort of natural
adaptation is far from adequate to constitute a dietetic guide. Not only
is it true that many substances accessible to human beings are injurious
and unwholesome, in spite of their agreeable taste; it is equally true
that many substances that are initially distasteful may be either
nourishing or remedial. Human beings find it necessary to supplement, or
even to supplant, the “beneficent guardianship” of taste by the
introduction of various other sources of information and criteria of
selection.
We do not find, however, that the sense of taste shows any evidence of
deterioration as the result of such loss of function. Probably never
before in the history of our race has there been such diligence and zeal
in ministering to the demands and satisfactions of our appetite. In the
preparation, marketing, and serving of food the appeal through
tastefulness and flavor stands second only to that through purity and
cleanliness. The situation is neatly stated by Jane Addams in the
following words: “Perhaps the neighborhood estimate (of their New
England kitchen) was summed up by the woman who frankly confessed that
the food was certainly nutritious, but that she didn’t like to eat what
was nutritious; that she liked to eat ‘what she’d ruther.’”
It is clear at once that the satisfactions of taste are pursued, either
secretly or openly, for their own sake, and often in obvious disregard
of their dietetic consequences. Shall we dismiss this pursuit as only an
instance of the search for pleasure in its own right or wrong, or is
there to be discerned a further function of taste experiences quite
aside from their guidance to eating, their warning of danger, and their
immediate sensory pleasure?
_Taste and Digestion_
Recent studies of the rôle of taste in the economy of the organism show
very decidedly that such an additional function, and a very important
one, must be recognized. These investigations have revealed the fact
that the pleasurable taste of food (along with its agreeable odor and
appearance) is responsible for the initiation of the first stages of the
process of digestion. Further, they have shown that disagreeable tastes
and odors (along with pain, fear, and other emotional excitement) may
effectually retard or even completely inhibit these very important
processes. Not only does the mouth “water” at the smell, or sight, or
thought, of delicious morsels, but the stomach itself responds, in an
anticipatory fashion, to the taste of agreeable substances placed in the
mouth. That “good digestion waits on appetite” is a physiological fact,
as well as an ancient proverb.
In the middle of the last century two observers in Leipsic reported the
pouring out of gastric juice at the mere sight or smell of a favorite
food in the case of “a hungry dog which had a fistulous opening through
the body wall into the stomach.” More recently it has been
experimentally shown that similar flow of gastric juice follows upon the
tasting of agreeable food, even if the food itself is not allowed to
reach the stomach. So relevant are these findings to the point we are
now considering that the following summary, by Cannon, of the work of
Pavlow may well be quoted in detail:
_Experimental Evidences_
“The feelings or affective states favorable to the digestive functions
have been studied fruitfully by Pavlow, of Petrograd, through ingenious
experiments on dogs. By the use of careful surgical methods he was able
to make a side pouch of a part of the stomach, the cavity of which was
wholly separate from the main cavity in which the food was received.
This pouch was supplied in a normal manner with nerves and blood
vessels, and, as it opened to the surface of the body, the amount and
character of the gastric juice secreted by it under various conditions
could be accurately determined. Secretion by that part of the stomach
wall which was included in the pouch was representative of the secreting
activities of the entire stomach. The arrangement was particularly
advantageous in providing the gastric juice unmixed with food. In some
of the animals thus operated upon an opening was also made in the
esophagus, so that when the food was swallowed it did not pass to the
stomach, but dropped out on the way. All the pleasures of eating were
thus experienced, and there was no necessity of stopping because of a
sense of fullness. This process was called ‘sham feeding.’ The
well-being of these animals was carefully attended to; they lived the
normal life of dogs, and in the course of months and years became the
pets of the laboratory.
Pavlow showed that the chewing and swallowing of food which the dogs
relished resulted, after a delay of about five minutes, in a flow of
natural gastric juice from the side pouch of the stomach—a flow which
persisted as long as the dog chewed and swallowed the food and continued
for some time after eating ceased. Evidently the presence of food in the
stomach is not a prime condition for gastric secretions, and, since the
flow occurred only when the dogs had an appetite and the material
presented to them was agreeable, the conclusion was justified that this
was a true psychic secretion.”
In several cases necessary operations on human beings have permitted of
observations similar to these experiments on dogs. Thus, Richet, who had
opportunity to observe such a case, “reported that whenever the girl
chewed or tasted a highly sapid substance, such as sugar or lemon juice,
while the stomach was empty, there flowed from the fistula a
considerable quantity of gastric juice.” Another observer, Hornborg,
“found that when the little boy whom he studied chewed agreeable food a
more or less active secretion of gastric juice invariably started,
whereas the chewing of an indifferent substance, as gutta-percha, was
followed by no secretion.”
Carlson has reported numerous similar observations on an adult. In the
case of this man the sight, smell, or thought of food, even when he was
hungry, was inadequate to cause the gastric juice to flow. Moreover,
“the mere act of chewing indifferent substances, and the stimulation of
the nerve endings in the mouth by substances other than those related to
food,” caused no secretion. But a few minutes after the taste organs
were stimulated by edible substances it was seen that not only did the
flow of gastric juice begin, but the “hunger contractions” of the
stomach were inhibited. Further, the secretion of gastric juice in this
patient was clearly seen to vary with the palatability of the food. The
chewing of bread and butter yielded a smaller flow than did the
mastication of meat, and the flow was always greatest during the chewing
of desserts, or on occasions when the food was said to be “unusually
fine.” Oranges, of which the patient was especially fond, produced a
greater flow than did pies, puddings, and other fruits. Carlson, in
reporting these observations, says: “There is no question but that the
mastication of a palatable dessert at the end of a meal serves to
augment and prolong the appetite secretion of the gastric juice.”
In referring to such cases Cannon has concluded: “All these observations
clearly demonstrate that the normal flow of the first digestive fluids,
the saliva and the gastric juice, is favored by the pleasurable feelings
which accompany the taste and smell of food during mastication, or which
are roused in anticipation of eating when choice morsels are seen or
smelled. These facts are of fundamental importance in the serving of
food, especially when, through illness, the appetite is fickle. The
degree of daintiness with which nourishment is served, the little
attentions to æsthetic details—the arrangement of the dishes, the small
portions of food, the flower beside the plate—all may help to render
food pleasing to the eye and savory to the nostrils, and may be the
deciding factors in determining whether the restoration of strength is
to begin or not.”
_The Function of Taste in the Organic Economy_
The preliminary nature of these anticipatory secretions of the digestive
juices is by no means an adequate measure of their ultimate importance.
Studies of the mechanism of digestion show that each stage, as it
occurs, either directly or indirectly, through its product, affords the
appropriate stimulus which evokes the following stage. Thus, continued
flow of gastric juice is provided for by the action of the preliminary
flow or its products on the walls of the stomach; and other juices, such
as the bile and the pancreatic, are in turn released by the action of
this continued flow.
The pleasurable sensations of taste are thus the initial stimulus to the
whole series of digestive processes. Even in the absence of hunger these
sensations seem potent to initiate the digestive mechanism. Among the
most interesting of recent physiological studies are those showing the
very great sensitivity of the important organic mechanisms, especially
those of secretion, to such experiences as shock, worry, fear, anger,
grief, excitement, and pain. All these factors tend to retard the
activity of the digestive system, while they may also be seen to
reënforce the activity of other mechanisms. As opposed to the effect of
these factors, pleasurable experiences connected with food serve not
only to guide the organism in its choice, but play an important part in
its effective appropriation and assimilation, through their action in
setting the digestive mechanisms in action, and in guaranteeing the
continuation of this action after the completion of the act of eating.
Music and dance, jest and general merriment, genial conversation and
cordial friendship, prosperity and individual success, fragrance, color,
bodily ease, and a clear conscience—these and all the other joys of life
play their part in promoting the bodily welfare of the organism.
Conspicuous and potent among these favoring influences are the
sensations of taste and the strongly toned feelings with which they are
so closely associated—“the satisfactions of the palate.” Even the
various “bitters” which are so commonly used as “appetizers” seem to owe
such efficacy as they may possess to the influence of their taste on the
preliminary flow of “appetite gastric.” Carlson has shown that these
bitters, introduced directly into the stomach in medicinal doses, have
no influence on the hunger mechanisms. In larger doses their effect is
inhibition of hunger. Acting in the mouth, they also retard the hunger
contractions of the stomach in proportion to their intensity as taste
stimuli. In so far, then, as “bitters” are “appetizing,” it is by virtue
of their taste qualities, rather than their medicinal properties, and
the act of swallowing them would seem to be superfluous.
------------------------------------------------------------------------