Pain, like other phenomena, was probably evolved for a particular purpose--
surely for the good of the individual; like fear and worry,
it frequently is injurious. What then may be its purpose?
We postulate that pain is one of the phenomena which result
from a stimulation to motor action. When a barefoot boy steps
on a sharp stone it is important that the injuring contact be
released as quickly as possible; and therefore physical injury pain
results and impels the required action. Anemia of the soft parts
at the points of pressure results from prolonged sitting or lying
in one position, and as a result pain compels a muscular action
that shifts the damaging pressure--this is the pain of anemia;
when the rays of the blazing sun shine directly upon the retina,
pain immediately causes a protective muscular action--the lid is closed,
the head turns away--this is light pain; when standing too close
to a blazing fire the excessive heat causes a pain which results
in the protective muscular action of moving away--this is heat pain;
when the urinary bladder is acutely overdistended the resultant
pain induces voluntary as well as involuntary muscular contraction--
this is evacuation pain; associated with defecation is a characteristic
warning pain, and an active pain which induces the required
muscular action--this, like the pain accompanying micturition,
is an evacuation pain; in obstruction of the urinary passages
and of the large and the small intestine the pain is exaggerated,
as is the accompanying muscular contraction--this is a pathologic
evacuation pain; when the fetus reaches full term and labor is
to begin, it is heralded by pain which is associated with rhythmic
contractions of the uterine muscle; later, many other muscles
take part in the birth and pain is associated with all these
muscular contractions--these are labor pains; when a foreign body,
be it ever so small, falls upon the conjunctiva or cornea there
results what is perhaps the acutest pain known, and quick and active
muscular action follows--this is special contact pain. Special pain
receptors are placed in certain parts of the nose, the pharynx,
and the larynx, the stimulation of which causes special motor acts,
such as sneezing, hawking, coughing. Curiously vague pains are
associated with the protective motor act of vomiting and with the sexual
motor acts--these may be termed nausea pains and pleasure pains.
We now see, therefore, that against the injurious physical contacts
of environment, against heat and cold, against damaging sunlight,
against local anemia when resting or sleeping, the body is protected
by virtue of the muscular action which results from pain.
Then, too, for the emptying of the pregnant uterus, for the evacuation
of the intestine and of the urinary bladder as normal acts,
and for the overcoming of obstructions in these tracts,
pain compels the required muscular actions, For passing gall-stones
and urinary calculi, urgent motor stimuli are awakened by pain.
For each of these diversified pains the consequent muscular action
is specific in type, distribution, and intensity. This statement
is so commonplace that we are apt to miss the significance and
the wonder of it. It is probable that every nerve-ending in the skin
and every type of stimulation represents a separate motor pattern,
the adequate stimulation of which causes always the same response.
Let us pass on to the discussion of another and perhaps even
more interesting type of pain, that associated with infection.
Not all kinds of infection are painful; and in those infections
that may be associated with pain there is pain only when certain
regions of the body are involved. Among the infections that are not
associated with pain are scarlet fever, typhoid fever, measles, malaria,
whooping-cough, typhus fever, and syphilis in its early stages.
The infections that are usually, though not always, associated with
pain are the pyogenic infections. The pyogenic infections
and the exanthemata constitute the great majority of infections
and are the basis of the discussion which follows.
I will state one of my principal conclusions first, _i.
e_., that the only types of infection that are associated with pain
are those in which the infection may be spread by muscular action
or those in which the fixation of parts by continued muscular
rigidity is an advantage; and, further, as a striking corollary,
that the type of infection that may cause muscular action when it
attacks one region of the body may cause no such action when it
attacks another region.
The primary, and perhaps the most striking, difference between
the painless exanthemata and the painful pyogenic infections is that
in the case of the exanthemata the protective response of the body
is a chemical one,--the formation of antibodies in the blood,
which usually produce permanent immunity,--while the response to the
pyogenic infections is largely phagocytic. In the pyogenic infections,
in order to protect the remainder of the body, which, of course,
enjoys no immunity, every possible barrier against the spread
of the infection is thrown about the local point of infection.
How are these barriers formed? First, lymph is poured out, then the part
is fixed by the continuous contraction of the neighboring muscles
and by the inhibition of those muscles that, in the course of their
ordinary function, would by their contractions spread the infection.
Wherever there is protective muscular rigidity there is also pain.
On the other hand, in pyogenic infections in the substance
of the liver, in the substance of the kidney, within the brain,
in the retroperitoneal space, in the lobes of the lung, in the chambers
of the heart and in the blood-vessels of the chest and the abdomen,
in all locations in which muscular contractions can in no way assist
in localizing the disease, pyogenic infections produce no muscular
rigidity and no pain. Apparently, therefore, only those infections are
painful which are associated with a protective muscular contraction.
This explains why tuberculosis of the hip is painful, while tuberculosis
of the lung is painless.
There is a third type of pain which modifies muscular action
in a curious way. We have already stated that local pain serves
an adaptive purpose. In this light let us now consider headache.
Headache is one of the commonest initiatory symptoms of the
various infections, especially of those infections which are
accompanied by no local pain and by no local muscular action.
In peritonitis, cholecystitis, pleurisy, arthritis, appendicitis,
salpingitis, child-birth, in obstructions of the intestinal
and the genito-urinary tract, in short, in those acute processes
in which the local symptoms are powerful enough to govern
the individual as a whole,--to make him lie down and keep quiet,
refuse food and possibly reject what is already in the stomach,--
in all these conditions there is rarely a headache, but in the diseases
in which local pain is absent, such as the exanthemata, typhoid fever,
and auto-intoxication, which have no dominating local disturbances
to act as policemen to put the individual to bed and to make him
refuse food that he may be in the most favorable position to combat
the oncoming disease, in such cases in which these masterful and
beneficent local influences are absent we postulate that headache
has been evolved to perform this important service.
On the hypothesis that it is good for the individual who is acutely
stricken by a disease or who is poisoned by autointoxication to rest
and fast, and that the muscular system obeys the imperial command
of pain, and in view of the fact that the brain is not only in constant
touch with the conditions of every part of the body but that it
is also the controlling organ of the body, one would expect that in
these diseases the major pain whose purpose it is to govern general
muscular action would be located in the head and there we find it.
How curious and yet how intelligible is the fact that, though a
headache may be induced by even a slight auto-intoxication,
an abscess may exist within the brain without causing pain.
When an obliterative endarteritis is threatening a leg with
anemic gangrene, or when one lies too long in the same position on
a hard bed, there is threatening injury from local anemia, and as a
result there is acute pain, but when the obliterative endarteritis
threatens anemia of the brain, or when an embolism or thrombosis has
produced anemia of the brain, there may be no accompanying pain.
The probable explanation of the pain which results in the first instance
and the lack of pain in the second is that in the former muscular action
constitutes a self-protective response, but in the other it does not.
Diseases and injuries of the brain are notoriously difficult
to diagnosticate. This may well be because it has always been so well
protected by the skull that there have been evolved within it few
tell-tale self-protective responses, so that in the presence of injury
and disease within itself the brain remains remarkably silent.
It should occasion no surprise that there are in the brain no receptors,
the mechanical stimulation of which can cause pain, because its bony
covering has always prevented the adaptive implantation within it
of contact pain receptors. Dr. Frazier tells me that in the course
of his operations on the brains of unanesthetized patients
he is able to explore the entire brain freely and without pain.
From my own experience I am able to confirm Dr. Frazier's observation.
In addition, the two-stage operation for the excision of the Gasserian
ganglion provides an observation of extraordinary interest.
If at the first seance the ganglion is exposed, but is not disturbed
except by the iodoform gauze packing, then on the following
day the gauze may be removed, the ganglion picked up, and its
branches and root excised without anesthesia and without pain.
The same statement and explanation may be made regarding the distribution
of pain receptors for physical contact within the parenchyma of the liver,
the gall-bladder, the abdominal viscera, the spleen, the heart,
the lungs, the retroperitoneal tissue, the deep tissue of the back,
the vertebrae, and in certain portions of the spinal cord.
Just what is the distribution of the receptors for heat and for cold
I am unable to state, but this much we do know, that without
anesthesia the intestines may be cauterized freely without the least
pain resulting, and in animals the cauterization of the brain causes
no demonstrable change in the circulatory or respiratory reactions.
It is probable therefore that the distribution of the pain receptors
for physical contact and for heat are limited to those parts of the body
that have been exposed to injurious contacts with environment.
Of special significance is the pain which is due to cold,
which increases muscular tone and produces shivering. The general
increase in muscular tone produces an interesting postural phenomenon:
the limbs are flexed and the body bent forward, a position which probably
is due to the fact that the flexors are stronger than the extensors.
As muscular action is always accompanied by heat production,
the purpose of the muscular contraction and the shivering
is quite certainly caused by cold to assist in the maintenance
of the normal body temperature.
We have now discussed many of the causes of pain and in each instance
we have found an associated muscular action which apparently
serves some adaptive purpose (Figs. 24 and 25). If we assume
that pain exists for the purpose of stimulating muscular reactions,
we may well inquire what part of the nervous are is the site of
the sensation of pain--the nerve-endings, the trunk, or the brain?
Does pain result from physical contact with the nerve-endings, with
the physical act of transmitting an impression along the nerve trunk,
or with the process within the brain-cells by which energy is released
to cause a motor act?
It seems most probable that the site of the pain is in the brain-cells.
If this be so, then what is the physical process by which the
phenomena of pain are produced? The one hypothesis that can be
tested experimentally is that pain is a phenomenon resulting from
the rapid discharge of energy in the brain-cells. If this be true,
then if every pain receptor of the body were equally stimulated
in such a manner that
{illust. caption = FIG. 25.--FEAR AND AGONY. "Amid this dread
exuberance of woe ran naked spirits wing'd with horrid fear."--
Dante's "Inferno," Canto XXIV, lines 89, 90. all the stimuli
reached the brain-cells simultaneously, the cells would find
themselves in equilibrium and no motor act would be performed.
But if all the pain receptors of the body but one were equally stimulated,
and this one stimu-lated harder than the rest, then the latter
would gain possession of the final common path, the sensation
of pain would be felt, and a muscular contraction would result.
It is well known that when a greater pain is thrown into
competition with a lesser one, the lesser is completely submerged.
In this manner the school-boy initiates the novice into the mystery
of the painless plucking of hair. The simultaneous, but severe
application of the boot to the blindfolded victim takes complete
and exclusive possession of the final common path and the hair
is painlessly plucked through the triumph of the boot stimulus over
the hair stimulus in the struggle for the possession of the final
common path. Another argument in favor of this hypothesis that
pain is an accompaniment of the release of energy in the brain-
cells is found in the fact that painless stimuli received through
the special senses may completely submerge the painful stimuli
of physical injury; for although the stimuli to motor action,
which are received through the senses of sight, hearing, and smell,
cause even more powerful motor action than those caused by
physical contact stimuli, yet they are not accompanied by pain.
Examples of this triumph of stimulation of the special senses over
contact stimulation are frequently seen in persons obsessed by anger
or fear, and to a less degree in those obsessed by sexual emotion.
In the fury of battle the soldier may not perceive his wound until
the emotional excitation is wearing away, when the sensation
of warm blood on the skin may first attract his attention.
Religious fanatics are said to feel no pain when they subject themselves
to self-injury. Now, since both psychic and mechanical stimuli cause motor
action by the excitation ofprecisely the same mechanism in the brain,
and since the more rapid release of energy from psychic stimuli
submerges the physical stimuli and prevents pain, it would seem
that pain must be a phenomenon which is associated with the process
of releasing energy by the brain-cells. Were physical injury inflicted
in a quiescent state equal to that inflicted in the emotional state,
great pain and intense muscular action would be experienced.
Now the emotions are as purely motor excitants as is pain.
The dynamic result is the same the principal difference being the greater
suddenness and the absolute specificity of the pain stimuli as compared
with the more complex and less peremptory stimuli of the emotions.
A further evidence that pain is a product of the release of brain-cell
energy is the probability that if one could pierce the skin at
many points on a limb in such a manner that antagonistic points
only were equally and simultaneously stimulated, then an equilibrium
in the governing brain- cells would be established and neither
pain nor motion would follow. An absolute test of this assumption
cannot be made but it is supported by the obtainable evidence.
We will now turn to a new viewpoint, a practical as well as a
fascinating one, which can best be illustrated by two case histories:
A man, seventy-eight years old, whose chief complaint was obstinate
constipation, was admitted to the medical ward of the Lakeside Hospital
several years ago. The abdomen was but slightly distended;
there was no fever, no increased leukocytosis, no muscular rigidity,
and but slight general tenderness. He claimed to have lost in weight
and strength during the several months previous to his admission.
A tentative diagnosis of malignant tumor of the large intestine was made,
but free movements weresecured rather easily, and we abandoned
the idea of an exploratory operation. The patient gradually failed
and died without a definite diagnosis having been made by either
the medical or the surgical service. At autopsy there was found
a wide-spread peritonitis arising from a perforated appendix.
A child, several years old, was taken ill with some indefinite disease.
A number of the ablest medical and surgical consultants of a leading
medical center thoroughly and repeatedly investigated the case.
Although they could make no definite diagnosis they all
agreed that the trouble surely could not be appendicitis
because there was neither muscular rigidity nor tenderness.
The autopsy showed a gangrenous appendix and general peritonitis.
How can these apparently anomalous cases be explained?
These two cases are illustrations of the same principle that underlies
the freedom from pain which results from the use of narcotics
and anesthetics, the same principle that explains the fact that
cholecystitis may occur in the aged without any other local symptoms
than the presence of a mass and perhaps very slight tenderness;
and that accounts in general for the lack of well-expressed disease
phenomena in senility and in infancy. The reason why the aged,
the very young, and the subjects of general paresis show but few
symptoms of disease is that in senility the brain is deteriorated,
while in infancy the brain is so undeveloped that the mechanism
of association is inactive, hence pain and tenderness,
which are among the oldest of the associations, are wanting.
Senility and infancy are by nature normally narcotized.
The senile are passing through the twilight into the night;
while infants are traversing through the dawn into the day.
Hence it is that the diagnosis of injury and disease in the extremes
oflife is beset by especial difficulties, since the entire body
is as silent as are the brain, the pericardium, the mediastinum,
and other symptomless areas. For the same reason, when a patient
who is seriously ill with a painful disease turns upon the physician
a glowing eye and an eager face, and remarks how comfortable he feels,
then the end is near. This is a brilliant and fateful clinical mirage.
When one reflects on the vast amount of evidence as to the origin
and the purpose of pain, he is forced to conclude that pain is
a phenomenon of motor stimulation, and that its principal role is
the protection of the individual against the gross and the microscopic
enemies in his environment. The benefits of pain are especially
manifested in the urgent muscular actions by means of which the body
moves away from physical injury; obstructions of the hollow
viscera are overcome; rest is compelled in the acute infections--
the infected points are held rigidly quiet, the muscles of the abdomen
are fixed, and harmful peristalsis is arrested in peritonitis;
while there is absolutely no pain in the diseases or injuries
which affect those regions of the body in which in the course
of evolution no pain receptors were placed, or in those diseases
in which muscular inhibition or contraction is of no help.
In a biologic sense pain is closely associated with the emotional stimuli,
for both pain and the emotions incite motor activity for the good
of the individual. The frequent occurrence of post-operative and
post- traumatic pain is accounted for by the fact that the operation
or the injury has lowered the threshold of the brain- cells to trauma;
the brain and not the local sensitive field is the site of the pain.
I have found that, by blockingthe field of operation with
local anesthesia, post-operative pain is diminished; that is,
since the local anesthesia prevents the strong stimuli of the
trauma from reaching the brain, its threshold is not lowered.
There is a close resemblance between the phenomena of pain habit,
of education, of physical training, of love and of hate. In education,
in pain habit, in all emotional relations, a low brain- cell threshold
is established which facilitates the reception of specific stimuli;
all these processes are motor acts, or are symbolic of motor acts,
and we may be trained to perceive misfortune and pain as readily as we
are trained to perceive mathematical formulae or moral precepts.
In each and every case, readiness of perception depends, as it seems to me,
upon a modified state of the brain-cells, their threshold especially,
the final degree of perception possible in any individual being perhaps
based on the type of potential molecules of which the brain is built.
We must believe also that every impression is permanent, as only thus
could an individual animal or a man be fitted by his own experience
for life's battles. LAUGHTER AND CRYING What is laughter?
What is its probable origin, its distribution, and its purpose?
Laughter is an involuntary rhythmic contraction of certain
respiratory muscles, usually accompanied by certain vocal sounds.
It is a motor act of the respiratory apparatus primarily, although if
intense it may involve not only the extraordinary muscles of respiration,
but most of the muscles of the body. There are many degrees
of laughter, from the mere brightening of the eyes, a fleeting smile,
tittering andgiggling, to hysteric and convulsive laughter.
Under certain circumstances, laughter may be so intense and
so long continued that it leads to considerable exhaustion.
The formation of tears is sometimes associated with laughter.
When integrated with laughter, the nervous system can perform
no other function. Crying is closely associated with laughter,
and in children especially laughter and crying are readily interchanged.
We postulate that laughter and weeping serve a useful purpose.
According to Darwin, only man and monkeys laugh (Fig. 26);
other animals exhibit certain types of facial expression accompanying
various emotions, but laughter in the sense in which that word
is commonly used is probably an attribute of the primates only,
although it is probable that many animals find substitutes for laughter.
The proneness of man to laughter is modified by age, sex, training,
mental state, health, and by many other factors. Healthy, happy children
are especially prone to laughter, while disease, strong emotions,
fatigue, and age diminish laughter. Women laugh more than do men.
The healthy, happy maturing young woman perhaps laughs most, especially
when she is slightly embarrassed. What causes laughter? Good news,
high spirits, tickling, hearing and seeing others laugh; droll stories;
flashes of wit; passages of humor; averted injury; threatened breach
of the conventions; and numerous other causes might be added.
It is obvious that laughter may be produced by diverse influences,
many of which are so unlike each other that it would at first sight
seem improbable that a single general principle underlies all.
Before presenting a hypothesis which harmonizes most of the facts,
and which mayoffer an explanation of the origin and purpose of laughter,
let us return for a moment to some previous considerations--
that man is essentially a motor being; that all his responses to
the physical forces of his environment are motor; {illust. caption
= FIG. 26.--LAUGHING CHIMPANZEE. "Mike," the clever chimpanzee
in the London Zoo, evidently enjoys a joke as well as any one else.
(Photo by Underwood and Underwood, N. Y.)}
that thoughts and words even are symbolic of motor acts;
that in the emotions of fear, of anger, and of sexual love
the whole body is integrated for acts which are not performed.
These integrations stimulate the brain-cells, the ductless glands,
and other parts, and the energizing secretions, among which are epinephrin,
thyroid and hypophyseal secretions, are thrown into the blood-stream,
while that most available fuel, glycogen, is also mobilized in the blood.
This body-wide preparation for action may be designated kinetic reaction.
The fact that emotion is more injurious to the body than is
muscular action is well known, the difference being probably caused
by the fact that when there is action the above-mentioned products
of stimulation are consumed, while in stimulation without action
they are not consumed and must be eliminated as waste products.
Now these activating substances and the fuel glycogen may be consumed
by any muscular action as well as by the particular muscular action
for which the integration and consequent stimulation were made;
that is, if one were provoked to such anger that he felt impelled
to attack the object of his anger, one of three things might happen:
First, he might perform no physical act but give expression to
the emotion of anger; second, he might engage in a physical struggle
and completely satisfy his anger; third, he might immediately engage
in violent gymnastic exercises and thus consume all the motor-producing
elements mobilized by the anger and thus clarify his body.
In these premises we find our explanation of the origin and purpose
of laughter and crying, for since they consist almost wholly
of muscular exertion, they serve precisely such clarifying purposes
as would be served by the gymnastic exercises of an angry man.
As it seems to me, the muscular action of laughter clears the system
of the energizing substances which have been mobilized in various
parts of the body for the performance of other actions (Figs. 27
to 29). If this be true, the first question that presents itself is,
Why is the respiratory system utilized for such a clarifying purpose?
Why do we not laugh with our feet and hands as well?
Were laughter expressed with the hands, the monkey might fall
from the tree and, if by the feet, man might fall to the ground.
He would at least be ataxic. In fact, laughter has the great
advantage of utilizing a group of powerful muscles which can be
readily spared without seriously interfering with the maintenance
of posture. Laughter, however, is only one form of muscular action
which may consume the fuel thrown into the blood by excitation.
That these products of excitation are often consumed by other motor
acts than laughter is frequently seen in public meetings when
the stamping of feet and the clapping of hands in applause gives
relief to the excitation (Fig. 30). Why the noise of laughter?
In order that the products of excitation may be quickly and
completely consumed, the powerful group of expiratory muscles must
have some resistance against which they can exert themselves strongly
and at the same time provide for adequate respiratory exchange.
The intermittent closure of the epiglottis serves this purpose admirably,
just as the horizontal bars afford the resistance against which muscles
may be exercised. The facial muscles are not in use for other purposes,
hence their contractions will consume a little of the fuel.
An audience excited by the words of an impassioned speaker undergoes
a body-wide stimulation for action, all of which may be eliminated
by laughter or by applause (Fig. 31).
Let us test this hypothesis by some practical examples.
The first is an incident that accidentally occurred in our laboratory
during experiments on fear which were performed as follows:
A keen, snappy fox terrier was completely muzzled by winding a broad strip
of adhesive plaster around his jaw so as to include all but the nostrils.
When this aggressive little terrier and the rabbit found themselves
in close quarters each animal became completely governed by instinct;
the rabbit crouched in fear, while the terrier, with all the ancestral
assurance of seizing his prey, rushed, upon the rabbit, his muzzle
always glancing off and his attack ending in awkward failure.
This experiment was repeated many times and each time provoked
the serious-minded scientific visitors who witnessed it
to laughter. Why? Because the spectacle of a savage little terrier
rushing upon an innocent rabbit as if to mangle it integrated
the body of the onlooker with a strong desire to exert muscular
action to prevent the cruelty. This integration caused a conversion
of the potential energy in the brain-cells into kinetic energy,
and there resulted a discharge into the blood-stream of activating
internal secretions for the purpose of producing muscular action.
Instantly and unexpectedly the danger passed and the preparation
for muscular action intended for use in the protection of the rabbit
was not needed. This fuel was consumed by the neutral muscular
action of laughter, which thus afforded relief.
A common example of the same nature is that encountered on the street
when a pedestrian slips on a banana peel and, just as he is
about to tumble, recovers his equilibrium. The onlookers secure
relief from the integration to run to his rescue by laughing.
On the other hand, should the same pedestrian fall and fracture
his skull the motor integration of the onlookers would be consumed
by rendering physical assistance--hence there would be no laughter.
In children almost any unexpected phenomenon, such as a sudden "booing"
from behind a door, is attended by laughter, and in like manner
the kinetic reaction produced by the innumerable threats of danger
which are suddenly averted, a breach of the conventions, a sudden
relief from acute nervous tension; a surprise--indeed, any excitant
to which there is no predetermined method of giving a physical response--
may be neutralized by the excitation of the mechanism of laughter.
In the same way the laughter excited by jokes may be explained.
An analysis of a joke shows that it is composed of two parts--
the first, in which is presented a subject that acts as a stimulus
to action, and the second, in which the story turns suddenly
so that the stimulus to action is unexpectedly withdrawn.
The subject matter of the joke affects each hearer according
to the type of stimuli that commonly excites that individual.
Hence it is that a joke may convulse one person while it bores another,
and so there are jokes of the classes, bankers' jokes, politicians' jokes,
the jokes of professional men, of the plebeian, of the artist, etc.
If the joke fails, the integration products of the excitation may
be used in physical resentment (Fig. 32).
Another type of laughter is that associated with the ticklish points
of certain parts of the body, the soles of the feet and certain
parts of the trunk and of the abdomen. The excitation of the
ticklish receptors, like pain, compels self-defensive motor acts.
This response is of phylogenetic origin, and may be awakened only
by stimuli which are too light to be painful. In this connection
it is of interest to note that a superficial, insect-like contact
with the skin rarely provokes laughter, and that the tickling
of the nasal, oral, and pulmonary tracts does not produce laughter.
The ticklish points that cause laughter are rather deeply placed,
and a certain type of physical contact is required to constitute
an adequate stimulus. That is, the contact must arouse a phylogenetic
association with a physical struggle or with physical exertion.
In the foot, the adequate stimuli for laughter are such contacts
as resemble or suggest piercing by stones or rough objects.. The
intention of the one who tickles must be known; if his intention
be playful, laughter results, whereas if injury be intended,
then an effort toward escape or defense is excited, but no laughter.
If deep tickling of the ribs is known to be malicious, it will excite
physical resentment and not laughter. Self-tickling rarely causes
laughter for the reason that auto-tickling can cause only a known
degree of stimulation, so that there results no excessive integration
which requires relief by the neutral muscular activity of laughter.
In fact, one never sees purposeful acts and laughter associated.
According to its severity, an isolated stimulus causes either
an action or laughter. The ticklish points in our bodies were
probably developed as a means of defense against serious attacks
and of escape from injurious contacts.
Anger, fear, and grief are also strong excitants and, therefore,
are stimuli to motor activity. It is obvious that whatever the excitant
the physico-chemical action of the brain and the ductless glands
cannot be reversed--the effect of the stimulus cannot be recalled,
therefore either a purposeful muscular act or a neutralizing act
must be performed or else the liberated energy must smoulder
in the various parts of the body.
It is on this hypothesis that the origin and the purpose of laughter
and crying may be understood. Even a superficial analysis of the
phenomena of both laughter and crying show them to be without any
external motor purpose; the respiratory mechanism is intermittently
stimulated and inhibited; and the shoulder and arm muscles, indeed,
many muscles of the trunk and the extremities are, as far as any
external design is concerned, purposelessly contracted and released
until the kinetic energy mobilized by excitation is utilized.
During this time the facial expression gives the index to
the mental state.
Crying, like laughter, is always preceded by a stimulation
to some motor action which may or may not be performed
(Figs. 33 and 34). If a mother is anxiously watching the course
of a serious illness of her child and if, in caring for it, she is
stimulated to the utmost to perform motor acts, she will continue
in a state of motor tenseness until the child recovers or dies.
If relief is sudden, as in the crisis of pneumonia, and the mother
is not exhausted, she will easily laugh if tired, she may cry.
If death occurs, the stimulus to motor acts is suddenly
withdrawn and she then cries aloud, and performs many motor
acts as a result of the intense stimulation to motor activity
which is no longer needed in the physical care of her child.
With this clue we can find the explanation of many phenomena. We can
understand why laughter and crying are so frequently interchangeable;
why they often blend and why either gives a sense of relief;
we can understand why either laughter or crying can come only
when the issue that causes the integration is determined; we can
understand the extraordinary tendency to laughter that discloses
the unspoken sentiments of love; we can understand the tears
of the woman when she receives a proposal of marriage from the man
she loves; we can understand why any averted circumstance,
such as a threatened breach of the conventions, which would have led
to embarrassment or humiliation, leads to a tendency to laughter;
and why the recital of heroic deeds by association leads to tears,
On the other hand, under the domination of acute diseases,
of acute fear, or of great exhaustion, there is usually neither
laughter nor crying because the nervous system is under the control
of a dominating influence as a result of which the body is so
exhausted that the excess of energy which alone can produce laughing
or crying is lacking.
A remarkable study of the modification of laughter and crying by disease
is found in that most interesting of diseases--exophthalmic goiter.
In this disease there is a low threshold to all stimuli.
That the very motor mechanism of which we have been speaking
is involved, is shown by an enormous increase in its activity.
There is also an increase in the size of certain at least of the
activating glands--the thyroid and the adrenals are enlarged and overactive
and the glycogen-producing function of the liver is stimulated.
The most striking phenomenon of this disease, however, is the remarkable
lowering of the brain thresholds to stimuli. In other words,
in Graves' disease the nervous system and the activating glands--
the entire motor mechanism--are in an exalted state of activity.
If this be true, then these patients should exhibit behavior
precisely contrary to that of those suffering from acute infection,
that is, they should be constantly clearing their systems of
these superabundant energizing materials by crying or laughing,
and this is precisely what happens--the flood-gates of tears are open
much of the time in Graves' disease--a disease of the emotions.
We have already interpreted pain as a phenomenon of motor activity.
When pain does not lead to muscular activity it therefore frequently
leads to crying or to moaning, just as tickling, which is equally
an incentive to motor activity, results in laughter if it does
not find full expression in action.
From the foregoing we infer that pain, the intense motor response
to tickling, and emotional excitation are all primitive biologic
reactions for the good of the individual, and that all have
their origin in the operation of the great laws of evolution.
If to this inference we add the physiologic dictum that the nervous
system always acts as a whole, and that it can respond to but one
stimulus at a time, we can easily understand that while diverse
causes may integrate the nervous system for a specific action,
if the cause be suddenly removed, then the result of the
integration of the nervous system may be, not a specific action,
but an undesigned muscular action, such as crying or laughter.
Hence it is that laughter and crying may be evoked by diverse
exciting causes. The intensity of the laughter or of the crying
depends upon the intensity of the stimulus and the dynamic state
of the individual.
The linking together of these apparently widely separated phenomena
by the simple law of the discharge of energy by association perhaps
explains the association of an abnormal tendency to tears with an
abnormally low threshold for pain (Fig. 36). In the neurasthenic,
tears and pain are produced with abnormal facility. Hence it is that,
if a patient about to undergo a surgical operation is in a state of fear
and dread before the operation, the threshold to all stimuli is lowered,
and this lowered threshold will continue throughout the operation,
even under inhalation anesthesia, because the stimulus produced by
cutting sensitive tissue is transmitted to the brain just as readily
as if the patient were not anesthetized. In like manner, the brain
may be sensitized by the administration of large doses of thyroid
extract prior to operation, the threshold to injury in such a case
continuing to be low to traumatic stimuli even under anesthesia.
Under the sensitizing influences of thyroid extract or of Graves'
disease the effect of an injury, of an operation, or of emotional
excitation is heightened. The extent to which the threshold to pain
or to any other excitant is affected by Graves' disease is illustrated
by the almost fatal reaction which I once saw result from the mere
pricking with a hypodermic needle of a patient with this disease.
As the result of a visit from a friend, the pulse-rate of a victim of this
disease may increase twenty beats and his temperature rise markedly.
I have seen the mere suggestion of an operation produce collapse.
As the brain is thus remarkably sensitized in Graves' disease, we find
that in these patients laughter, crying, emotional disturbances,
and surgical shock are produced with remarkable facility.
I hope that even this admittedly crude and imperfect consideration
of this subject will suggest the possibility of establishing
a practical viewpoint as to the origin and purpose of pain,
of tickling, and of such expressions of emotion as laughter and crying,
and that it may help us to understand their significance in health
and in disease.
THE RELATION BETWEEN THE PHYSICAL STATE OF THE BRAIN-CELLS AND
BRAIN FUNCTIONS--EXPERIMENTAL AND CLINICAL[*]
[*] Address before The American Philosophical Society, April 18, 1913.
The brain in all animals (including man) is but the clearing-house
for reactions to environment, for animals are essentially motor
or neuromotor mechanisms, composed of many parts, it is true,
but integrated by the nervous system. Throughout the phylogenetic history
of the race the stimuli of environment have driven this mechanism,
whose seat of power--the battery--is the brain.
Since all normal life depends upon the response of the brain
to the daily stimuli, we should expect in health, as well
as in disease, to find modifications of the functions and the
physical state of the component parts of this central battery--
the brain-cells. Although we must believe, then, that every
reaction to stimuli, however slight, produces a corresponding
change in the brain-cells, yet there are certain normal, that is,
non-diseased, conditions which produce especially striking changes.
The cell changes due to the emotions, for example, are so similar,
and in extreme conditions approach so closely to the changes produced
by disease, that it is impossible to say where the normal ceases
and the abnormal begins.
In view of the similarity of brain-cell changes it is not strange
that in the clinic as well as in daily life, we are confronted
constantly by outward manifestations which are so nearly
identical that the true underlying cause of the condition in
any individual case is too often overlooked or misunderstood.
In our laboratory experiments and in our clinical observations
we have found that exhaustion produced by intense emotion,
prolonged physical exertion, insomnia, intense fear, certain toxemias,
hemorrhage, and the condition commonly denominated surgical shock,
produce similar outward manifestations and identical brain-cell changes.
It is, therefore, the purpose of this paper to present the definite
results of laboratory researches which show certain relations
between alterations in brain functions and physical changes
in the brain-cells.
Fear.--Our experiments have shown that the brain-cell changes due
to fear may be divided into two stages: First, that of hyperchromatism--
stimulation; second, that of hypochromatism--exhaustion (Figs. 5 and
13). Hyperchromatism was shown only in the presence of the activating
stimuli or within a very short time after they had been received.
This state gradually changed until the period of maximum exhaustion
was reached--about six hours later. Then a process of reconstruction
began and continued until the normal state was again reached.
Fatigue.--Fatigue from overexertion produced in the brain-cells
like changes to those produced by fear, these changes being
proportional to the amount of exertion (Fig. 4). In the extreme
stage of exhaustion from this cause we found that the total
quantity of Nissl substance was enormously reduced.
When the exertion was too greatly prolonged, it took weeks or
months for the cells to be restored to their normal condition.
We have proved, therefore, that in exhaustion resulting from emotion
or from physical work a certain number of the brain-cells are
permanently lost. This is the probable explanation of the fact
that an athlete or a race-horse trained to the point of highest
efficiency can reach his maximum record but once in his life.
Under certain conditions, however, it is possible that, though some
chromatin is forever lost, the remainder may be so remarkably developed
that for a time at least it will compensate for that which is gone.
Hemorrhage.--The loss of blood from any cause, if sufficient to reduce
the blood-pressure, will occasion a change in the brain-cells, provided
that the period of hypotension lasts for more than five minutes.
This time limit is a safeguard against permanent injury
from the temporary hypotension which causes one to faint.
If the hemorrhage be long continued and the blood-pressure be low,
there will be a permanent loss of some of the brain-cells. This
explains why an individual who has suffered from a prolonged
hemorrhage will never again be restored to his original powers.
Drugs.--According to their effect upon the brain-cells, drugs
may be divided into three classes: First, those that stimulate
the brain-cells to increased activity, as strychnin (Fig. 37);
second, those that chemically destroy the brain-cells, as alcohol
and iodoform (Figs. 38 and 39); third, those that suspend the functions
of the cells without damaging them, as nitrous oxid, ether, morphin.
Our experiments have shown that the brain-cell changes induced
by drugs of the first class are precisely the same as the cycle
of changes produced by the emotions and by physical activity.
We have found that strychnin, according to the dosage, causes convulsions
ending in exhaustion and death; excitation followed by lassitude;
stimulation without notable after-results; or
{illust. caption = A, Section of Cerebellum of Normal Dog. C, Section of
Cerebellum of Dog after Repeated Doses of Strychnin. FIG. 37.--
BRAIN-CELLS SHOWING STAGE OF HYPERCHROMATISM FOLLOWED BY CHROMATOLYSIS
RESULTING FROM THE CONTINUATION OF THE STIMULUS. (Camera lucida
drawings.)increased mental tone; while the brain-cells accurately
display these physiologic alterations in proportional hyperchromatism
in the active stages, and proportional chromatolysis in the stages
of reaction. The biologic and therapeutic application of this fact
is as obvious as it is important.
In our experiments, alcohol in large and repeated dosage caused
marked morphologic changes in the brain-cells which went as far
even as the destruction of some of the cells (Fig. 39). Ether,
on the other hand, even after five hours of administration,
produced no observable destructive changes in the brain-cells.
The effect of iodoform was peculiarly interesting, as it was the only
drug that produced a rise of temperature. Its observed effect upon
the brain-cells was that of wide-spread destruction.
Infections.--In every observation regarding the effect of pyogenic
infections on dogs and on man we found that they caused definite
and demonstrable lesions in certain cells of the nervous system,
the most marked changes being in the cortex and the cerebellum
(Fig. 40). For example, in fatal infections resulting from
bowel obstruction, in peritonitis, and in osteomyelitis, the real
lesion is in the brain-cells. We may, therefore, reasonably conclude
that the lassitude, the diminished mental power, the excitability,
irritability, restlessness, delirium, and unconsciousness which may
be associated with acute infections, are due to physical changes
in the brain-cells.
Graves' Disease.--In Graves' disease the brain-cells show marked
changes which are apparently the same as those produced by overwork,
by the emotions, and by strychnin. In the postmortem examination
of one advanced case it was found that a large number of brain-cells
were disintegrated beyond the power of recuperation, even had
the patient lived. This is undoubtedly the reason why a severe case
of exophthalmic goiter sustains a permanent loss of brain power.
Insomnia.--The brains of rabbits which had been kept awake for one
hundred hours showed precisely the same changes as those shown
in physical fatigue, strychnin poisoning, and exhaustion from
emotional stimulation. Eight hours of continuous sleep restored
all the cells except those that had been completely exhausted.
This will explain the permanent ill effect of long-continued insomnia;
that is, long-continued insomnia permanently destroys a part
of the brain-cells just as do too great physical exertion,
certain drugs, emotional strain, exophthalmic goiter, and hemorrhage.
We found, however, that if, instead of natural sleep, the rabbits
were placed for the same number of hours under nitrous oxid anesthesia,
not only did the brain-cells recover from the physical deterioration,
but that 90 per cent. of them became hyperchromatic.
This gives us a possible clue to the actual chemical effect of sleep.
For since nitrous oxid owes its anesthetic effect to its influence
upon oxidation, we may infer that sleep also retards the oxidation
of the cell contents. If this be true, then it is probable
that inhalation anesthetics exert their peculiar influence upon
that portion of the brain through which sleep itself is produced.
If nitrous oxid anesthesia and sleep are chemically identical, then we
have a further clue to one of the primary mechanisms of life itself;
and as a practical corollary one might be able to produce artificial
sleep which would closely resemble normal sleep, but which would
have this advantage, that by using an anesthetic which interferes with
oxidation the brain-cells might be reconstructed after physical fatigue,
after emotional strain, or after the depression of disease.
In the case of the rabbit in which nitrous oxid was substituted
for sleep, the appearance of the brain-cells resembled that in
but one other group experimentally examined--the brain-cells
of hibernating woodchucks.
Insanity.--Our researches have shown that in the course of a fatal
disease and in fatal exhaustion, however produced, death does not
ensue until there is marked disorganization of the brain tissue.
In the progress of disease or exhaustion one may see in different
patients every outward manifestation of mental deterioration,
manifestations which, in a person who does not show any other sign of
physical disease, mark him as insane. Take, for example, the progressive
mental state of a brilliant scholar suffering from typhoid fever.
On the first day of the gradual onset of the disease he would
notice that his mental power was below its maximum efficiency;
on the second he would notice a further deterioration, and so
the mental effect of his disease would progress until he would
find it impossible to express a thought or to make a deduction.
No one can be philanthropic with jaundice; no one suffering
from Graves' disease can be generous; no mental process is possible
in the course of the acute infectious diseases. Just prior to death
from any cause every one is in a mental state which, if it could
be continued, would cause that individual to be judged insane.
If the delirium that occurs in the course of certain diseases
should be continued, the patient would be judged insane.
In severe cases of Graves' disease the patient is insane.
Individuals under overwhelming emotion may be temporarily insane.
Every clinician has seen great numbers of cases in which insanity
is a phase of a disease, of an injury, or of an emotion.
The stage of excitation in anesthesia is insanity.
The only difference between what is conventionally called insanity
and the fleeting insanity of the sick and the injured is that of time.
We may conclude, therefore, what must be the brain-picture of the person
who is permanently insane. This _a priori_ reasoning is all that
is possible, since the study of the brain in the insane has thus far
been confined to the brains of those who have died of some disease.
And it is impossible to say which changes have been produced by the
fatal disease, and which by the condition which produced the insanity.
The only logical way by which to investigate the physical basis
of insanity would be to make use of the very rare opportunities
of studying the brains of insane persons who have died in accidents.
Our experiments have proved conclusively that whether we call a person
fatigued or diseased, the brain-cells undergo physical deterioration,
accompanied by loss of mental power (Figs. 40 to 43). Even to the minutest
detail we can show a direct relationship between the physical state
of the brain-cells and the mental power of the individual, that is,
the physical power of a person goes _pari passu_ with his mental power.
Indeed, it is impossible to conceive how any mental action,
however subtle, can occur without a corresponding change in the
brain-cells. It is possible now to measure only the evidences of
the effects on the brain-cells of gross and violent mental activity.
At some future time it will doubtless be possible so to refine
the technic of brain-cell examinations that more subtle changes
may be measured. Nevertheless, with the means at our disposal
we have shown already that in all the conditions which we
have studied the cells of the cortex show the greatest changes,
and that loss of the higher mental functions invariably accompanies
the cell deterioration.