If learning is a matter of the mind, then there is a mind in every part of an organism. There is the "visceral learning" of bowel-habits, of vascular responses to foreboding (palpitations of the heart, or blushing), of sexual responses to anticipated arousal. Blushing, constipation, hyperventilating are involuntary behaviours of the mind/body. Most of the involuntarily learned functions and behaviours can be unlearned by remedial programs which are provided by paramedical specialists in a body-oriented therapy.
An apparently involuntary function that can be brought under partial voluntary control, is activation or arousal. A drowsy or sleepy state is not a suitable condition to learn perceptual and motor skills. When body and mind are activated to the right degree the senses are alert, the coordinating nervous system and the muscles are responsive. When attention is low, there is no keenness of observation, no attempt at discovery and fine discrimination, no interest, no probing, and hardly retention and storage in memory. Yet all this is required for perceptual and cognitive learning and for developing communicative skills.The arousal system, as expected, has a concentric organisation. The activating system consists of layers that can be identified as
The first has its base close to the core functions. It promotes a wakeful state and a readiness of the body for action; the brain's substrate for this function is the reticular system in the brainstem. The substrate for focussed attention is the limbic system. This part of the brain is more differentiated and envelops the brainstem. The limbic system is an old part of the cerebral cortex, originally connected to the sense of smell, where the meaning of perceptual information is evaluated for its attention value. If found relevant, the outcome is transformed into the kind of motivation that leads to the appropriate form of action. For example an attractive smell elicits approach, a repugnant smell avoidance. Information from the other senses are also processed by the limbic system. In an infant, the sound of a spoon in a cup is associated with food and elicits a positive expectation, whereas the sight of a strange face may inspire apprehension.
Just as there are two layers of activation there are two modes of learning, the functional layers of which envelop each other:
Emotional and motivational learning by classical conditioning, mainly involves the central part of the brain and the limbic system. It is attended by adjustments in the "vegetative" or autonomous nervous system; messages, such as an arousal response, are relayed by neuro-endocrine messengers. Glands and smooth muscles are the effector organs. Increased ortho-sympathetic innervation (by the autonomous system) leads to increased circulation of adrenal hormones, and prepares the body for sustained effort. An aroused state of the autonomous system is elicited by signals which are interpreted by the individual as exciting. Vice versa the arousal state lowers the thresholds of the mind for strong emotional reactions such as anxiety and anger.
Type II, instrumental or operant learning, is mediated by the brain's cortex and the sensomotor system of nerve-tracks and muscles. It uses striped muscles as effector organs. This is the fast responding "animal" system. Basically it implements the needs and motives generated by the "vegetative" or autonomous system, that oscillates in a slower rhythm.
Learning, in the words of Pringle, is an "evolutionary" increase in complexity of rhythm, analogous to the increase of structural complexity which occurs in organic evolution. Oscillators within the neuronal system are more or less coupled by their sharing a number of neurons and this leads to partial synchronisation. A change in one oscillator will change the pattern of all the others until a new equilibrium in the whole system is reached. External stimulation leads to the formation of rhythmic patterns specific for the release of a certain response.
A high level of arousal prepares the individual for exertion but may interfere with fine motor activities e.g. by causing a tremor. One of the input processing systems may become overloaded and then is not able to cope with the influx of information, either because the information is of an unusual kind or comes in excessive quantities. This then leads to a temporary breakdown of coordination and to activation of a more primitive zone of adaptation and defence (regression, Map 6.1). It may lead to tremor, rigidity, inhibited coordination of "nervous" origin, which all have great relevance for voice- and speech pathology, especially in speech- and voice neuroses (stuttering and spastic dysphonia). It may also lead to a more permanent inhibition of development.
Derived from the two elementary forms of learning are other forms such as vicarious learning and learning by association, by imagination, by imitation, which take place at a high cognitive level.
Concentric organisation is designed to maintain plasticity of the otherwise stable memory system: we need fast and slow systems that interact with each other. An attentional system keeps stable representations of familiar features of the environment. A (faster) orienting subsystem responds to novelty and resets the attentional system when a new and unfamiliar event occurs. The system's hierarchy is acting in opposite directions: bottom-up input patterns are compared with active top-down feature patterns. This is one of the claims of Grossberg's Adaptive Response Theory.
What happens in learning is that there is coupling of slow and fast responding parts of the central nervous system (CNS). The slower system drives the action of the faster system. The drive system transmits the genetic and other stable information from the core of the organism towards the more outer layers which receive their information from the environment. The drive system sets the parameters which the faster executive system is implementing. This is the neurophysiological base of the "two-factor" theory of learning.
Sometimes the immune system, acting as a physiological drive, initiates a behavioural sequence. Suppose you have been infected by a virus and run a fever: the body thermostat is set higher (factor 1, the autonomous system) and your motor system is instrumental in attaining the new temperature level, by shivering, by pulling up the blanket, by asking for an extra blanket: note that the use of language and speech will help to raise one's temperature and that language is instrumental (factor 2, the sensomotor system) in supplementing a regulatory function! The immune system responds more slowly than the vegetative regulatory system and is connected to the CNS via the autonomous/neuro-endocrine system (time-window to the right in Map 4.4.2). The immune system, a hidden factor in the learning hierarchy, watches over the individuals' physical health and integrity. Note the difference in the time constant of the response systems, as expressed in days, hours, minutes, seconds and fractions of seconds. The time constant, as defined earlier, is a measure of the time a system needs to resume it's stability when its equilibrium has been disturbed. Just as in the neural system, there are slow and fast responding subdivisions in the immune system: the cellular responses oscillating in a slower rhythm than the humoral responses. These responses are mutually dependent.
In living systems equilibria are maintained in a dynamic fashion: oscillating around a mean value. This makes them sensitive to stimuli from their immediate environment, and by responding they in turn exert influence on neighbouring systems. Living systems interact with each other and, by coupling into networks, gradually grow more complex (Pringle 1951, 1968). Such interactions are at the root of societal growth (language, organisations, institutions) , of development (interaction of cells and messenger molecules) and learning (oscillatory loops between neurons).
Another example of the continuity of systems: the immune system has a role in shaping the functions of the brain in a very early stage of development. The directing influence of the immune system has been explored especially with regard to cognitive functions and language. An intriguing finding is that in many dyslectic families and in about 20 % of our stuttering population, an (atopic) predisposition for hyper-reactivity to common allergens has been shown to exist and may have influenced the course of the disorders (Map 18).
|A fundamental decision, vital for all|
living beings, is the choice between
The word meaning is used at many different levels. Words of course have a meaning, and, more elementary, there is a meaning attached to perceived olfactory, tactual, auditory or visual signals. Situations are classified according to the signals and their consequences, as positive (to be accepted) or as negative (to be avoided). The elementary discrimination between good and bad food is based in part on inborn patterns of discernment and in part on judgement acquired by experience. The inborn discernment is acquired in the course of evolution (phylogeny), in contrast to a meaning based on experience that is acquired in the school of (ontogenic) life. Meaning arises first from relations to bodily needs, later from emotional, social, moral and spiritual needs (Chapter 8). Hence it is clear that meaning is not always universal but is sometimes stricly personal. Not all early experiences are nourishing, some are really bad. For that reason every new-born child must learn from the beginning how to discriminate nourishing from evil stimuli, and how to handle poisonous, adverse stimulation. Remembering and storing the lessons from early experiences is just as important for the central nervous system as the gradual immunisation is for the lymphoid system.
During growth and development of an embryo the decisions are made at the chemical/cellular level and are determined genetically, e.g. by the codes of the histo-compatibility (or HLA) complex. In a further stage immune markers of the self are used to recognise and discriminate between useful and harmful antigens. Antibodies are formed that will memorise and recall every early experience for as long as the individual will live. The immune system continuously communicates with the environment: scanning and sniffing, rejecting and approving, on the basis of genetic rules that have been refined by the traces of past experiences. The lymphoid system has learned to resist adverse factors and to make good use of the favourable factors in the environment, and in so doing it assures the physical health of the individual.
In various and more differentiated ways the neuronal system (CNS) does the same for the mental health of the individual. It scans, recognises, evaluates and selects, it approaches nourishing and avoids harmful stimulation. Communication and defence: the two are one.
Map 6.3 is again about the two-way learning process. It shows in its right half that appropriate responses are selected by the circumstances in which they occur. In behaviourist jargon: response-selection is controlled by the environment. The display in its left half shows that anticipated effects of certain actions are remembered as motives. The saying "Love is the anticipation of pleasure" reveals that love is a potent motivator. When imagined stimuli are labelled as desirable they acquire a positive "meaning". Another motive: "Social disapproval must be avoided at all costs": the thought of being rebuked in public is so aversive that all actions that could lead to it are avoided. Such motivating responses as apprehension or aversion are indicated by the small r's. The capital R's on the right are the instrumental actions that implement the drives and motives on the left.
|aversion||-------------||turns away from|
The learning process that involves meaning and motivation results in a more refined structure of emotions. Stimuli which on the basis of earlier experience are judged as relevant for welfare give rise to positive feelings: optimism, assertiveness, assiduity and to resourceful activity. Input that on the basis of past experience is judged as valueless or harmful gives rise to negative feelings of boredom, helplessness, depression and apathy and to absence of resourceful activity. Symptoms of depression that are very similar to those in humans have been experimentally induced in dogs by submitting them to inescapable unconditioned punishing experiences (Seligman 1975). The resulting symptoms were: cognitive distortion (the animal does not notice or recognise signs that can lead to his rescue), motivational deficit (little arousal, stops trying), affective disturbance. It was possible to make an end to this negative circle by external help. After showing the dog repeatedly how he could escape the punishment by climbing over the fence, by actually lifting him and carrying him to safety, he finally learned to climb out himself.
The principle that governs learning is the same as the evolution-principle: the response to an environmental challenge improves by variation and selection, and this gradually leads to ever more appropriate responses. An evolving species continuously improves its adaptation to its usual environment, its ecological niche. An individual during its life-time improves his individual adjustment to the particular environment in which he happens to grow up. Selection from a prolific variety of possibilities is a feature that learning (in the individuals ontogeny) has in common with evolution (in the phylogeny of the species). The environment assists in shaping the individuals' skills by rewarding the best adapted varieties in the repertoire of behavioural responses. Different types of learning are:
'A-B-C ' is a mnemonic device that permits a broad categorisation of the learning process. It stands for:
A: antecedent events, genetic constitutional and personality factors, attitudes, anticipations, the accompanying arousal, the challenging stimulus in the environment (A elicits B)
B: a behaviour; the individual responds to a stimulus; the response is often motivational or emotional and involuntary (factor 1) and is followed by instrumental behaviour appropriate to the situation (factor 2)
C: the consequences of the behaviour: the environment reacts to the response in a positive or neutral or negative way, thus reinforcing a habit or not reinforcing it. Consequent events can be either rewarding or punishing.
Events (A) antecede the behaviour (B) and the behaviour is followed by consequences (C). Consequences shape future behaviour. By becoming associated with antecedent events they also cause anticipation. When one has had a bad experience when answering a phone-call one will try to avoid picking up the telephone in future. On hearing the ringing sound one already becomes apprehensive.
In classical conditioning (type I) signals from the environment acquire a meaning. Drives and motives are goal-directed responses. They stem either from internal needs or environmental challenges. Type II learning concerns perceptual and motor skills that implement the type I motives. By repeated experiences and by trial-and-error (type II) an individual learns to anticipate the effects of its own behaviour. He learns to scan, to select, to choose his preferred environment, in short he increases his measure of control.
Focussed attention, and an adequate degree of general arousal are necessary for various sorts of learning and for retention in memory:
An adequate degree of general arousal and attention response is called facilitating stress. It is elicited by challenges that do not surpass the limits of the individual's coping capacity. If learning is to take place, some sort of reward has to follow the finishing of the task. Passing from a state of uncertainty to one of assurance may in itself be sufficiently rewarding. In the context of non-verbal communication, a smile or other sign of recognition may be the reward. It confirms the child's expectations that it is competent in relating to it's parent and in exerting some influence over it's environment.
By growth and differentiation, every child keeps increasing it's possibilities to interact with the world. It constantly adds new "layers" to it's personal behavioural equipment, the latest of which are vulnerable and not yet stable. As the new behaviour is exposed to the environment it can be put to severe tests. In the case of a massive aversive stimulation for which it is not yet prepared, the new behaviour may fail and be discontinued. Progression stops and regression takes its place.
People differ as to their nervous excitability and their immune vigilance. On the one hand we see individuals who have a neuronal constitution with high excitation thresholds (we label these persons extroverts). Only when repeatedly or strongly stimulated do they respond with arousal and attention. In the ancient terms of Heymans they would belong to the phlegmatic temperament. The analogous property of the immune system is low vigilance and low reactivity. On the other hand there are people with an overly sensitive and/or overly reacting neuronal and autonomous constitution (introverts). They react strongly to stimulation and easily become overexcited. The analogous immune temperament is high vigilance and overreaction.
Anxiety and excitement can incapacitate the faculty of focussed attention and of accurate observation. Overreacting with nervousness and tenseness is a cause for inhibitory or blocking stress-reactions. If overreactions occur frequently they become a hazard for cognitive development. Educators at home and in the schools should be aware of the differences in emotional temperament between children (Chapter 7).
Since life is full of unpredictable events, system-overload cannot always be prevented. J.G.Miller (1965) presented a thesis about hierarchically ordered systems, that predicts the hazards we have just mentioned. If a high organisation level of the system reaches the limits of its competence to handle information (= overflow), the next lower level will take over the coordinating task. This has consequences for the systems we have discussed: the genetic system, the immune, the neuronal and the language systems. Genetic regression may secure the survival of a species when dramatic and long lasting changes in the environment put heavy demands on adaptability. Since this subject is beyond the scope of this book we'll limit the discussion to the three remaining systems of adaptation and defence. By keenly observing the effect of overflow, the hierarchical order in the systems may reveal itself. Regression to an organized response of a lower order is often reinforced by its immediate beneficial effects and, by learning, may become a permanent feature. It seems plausible that habit formation can take place in the lymphoid, as well as in the neuronal and the language system. This will be illustrated in the paragraphs that follow.
The allergic response is a primitive, pre-immune defence reaction in higher vertebrates. On a lower level than the more differentiated immune responses, it shares several chemical processes with inflammation and wound-repair, including activation of the complement-system: i.e. rather direct and elementary rescue-responses meant for emergencies, to stop bleeding and to seal off tissue-damage. Parts of the rather explosive complement-system are touched off in an allergic emergency response, in contrast to the more differentiated and subtle responses that immunity supplies (Map 5.2). When over-stimulation by an unmanageable quantity of an antigen prevents proper immunity to develop, the system may regress to an allergic response. The (genetically) vulnerable 15% of humanity is very likely to suffer the consequences of such regression. These people are genetically predisposed to manifest so-called atopic reactions. They will suffer from either allergy (regression in the lymphoid system) or neuroticism (regression in the neuronal system, see next paragraph) or of both. Patients who alternate bouts of eczema and asthma and episodes of tension/anxiety syndrome are not at all rare. People with a more robust genetic constitution can also be affected in this way. Although the probability is much less a regressive reaction may be provoked if the excessive stimulation continues long enough, or if it happens during a temporary lowering of the defence system. Even in the absence of hereditary traits for allergy, a baker for example will sooner or later develop baker's eczema, if the exposure to the allergen is intense enough.
A neuronal analogy to allergy is overreacting, when the individual cannot handle a certain situation. It occurs more frequently in infants than in adults. When confronted with a threatening situation with which it has not yet learned to cope, an infant is subject to information-overflow by massive stimulation. The child enters an emotional state of frustration, fear and anger. Since he cannot handle the unfamiliar or overwhelming stimulation, he resorts to primitive means for rejection and avoidance. In animals any behaviour related to fight or flight is called agonistic behaviour, a term which in this case applies to humans as well. Every normal child will develop neurotic fears and a state of anxiety if he has met with threatening and stressful events, while being insufficiently protected by parental bonding. Agonistic behaviour as observed in children consists of aggression, tantrums, shouting, when motivated by the tendency to 'fight'. In the case of 'flight' it consists of submission, withdrawal and weeping. If agonistic responses are of short duration and not frequent, recovery to well-differentiated coping behaviour will likely occur. If however the agonistic episodes are reinforced by rewarding effects, they may become 'habits' and this is detrimental the development of the child's adaptation and defence faculties. A person who has suffered frequent regressions in early childhood can be damaged for life. It is a source of what used to be called neurotic maladjustment. The next paragraph gives more details how the road to normal resiliency may become blocked.
When does an (agonistic) regression become a permanent learned feature? With respect to the immune system we know that about 15 % of the entire population has a hereditary tendency to develop allergies for common constituents of the environment such as grass pollen and dust produced by the excrements and remains of house mites. This tendency is called atopy and depending on the "learning history" of the patients' immune system it may or may not become manifest. When exposure to antigens is gradual and in moderate doses, especially when the breast-fed infant is still under the protection of maternal antibodies, the immune cognition has a good chance to develop well. If such is the case antigens will be met by properly differentiated antibody-responses without allergic interference.
With respect to the neuronal system we assume that, analogous to the 15 % atopics in the population, there is a similar proportion of vulnerable people who are prone to neuroticism. An exact percentage cannot be given, since symptoms of neuroticism are not sharply defined. According to H.Eysenck, these people have a nervous system that is easily tired. In order to protect themselves against overstimulation they will resort more readily to introversion. A well administered course of stress-immunisation may prevent the development of neurotic fears or attitudes. Care must be taken that stressors are administered in such quantities as the child can manage. This means for example that they may suffer separation from their mother for short periods, and then, when this can be tolerated, for gradually longer periods, never exceeding the child's limits. Introvert infants are more vulnerable than their extravert counterparts, who thrive on stimulation and excitement. When, as happens all too easily in introverted children, the limits of tolerance are regularly exceeded, agonistic behaviour that should have been reserved for moments of emergency, becomes a part of daily life. Then regressive agonistic behaviour becomes a habit and for these children it is their only defence to survive the pressures of the environment. "Nervousness" then can be defined as a tendency to fall back into agonistic behaviour patterns. The tendency is learned, on the basis of genetic probability. Fortunately this also means that it can be prevented by proper management, that is: careful immunisation for stress.
Consider the following examples. Early bonding (attachment) to the caregiver offers protection for risk-free personal development, just as maternal immune-globulines during the period of breast feeding offer protection for gradual immune development. Unfortunately, there are circumstances under which mother and child fail to develop mutual attachment: birth in a strictly regimented clinic (early separation), illness of the mother, hospitalisation of the mother or the child. Failure of bonding during infancy is a heavy risk for normal development. Yet another risk factor that is little known was discovered by us. We have evidence that an early atopic eczema and/or bronchial wheezing has been the only demonstrable cause of developmental brain dysfunctions. It seems at first sight an unlikely connection. In the light of the attachment theory the consequences of eczema and bronchial obstruction can however become meaningful. A painful skin eruption puts a heavy strain on the mother-child relationship. Touching and caressing, which normally delights a baby and confirms its identity, is by reason of the tenderness of the skin transformed into a highly disagreeable form of contact. Handling the baby, normally a positive but now a painful experience, provokes aversion and avoidance responses on the part of the child. Bonding is a reciprocal process, and a mother who has been rejected repeatedly by her baby is profoundly disoriented and unhappy. If the eczematous condition lasts for more than a few weeks, irreversible emotional damage may already have occurred on both sides of the mother-child dyad.
We have heard similar observations from families with a wheezing child. Mothers were worried or felt sorry for their babies, and found it impossible to be as cheerful and happy as they used to be when the baby was healthy. Instead of a bond of mutual rejoicing there is anxiety and apprehension. Also, when professional caretakers take over the responsibility or the child, the mother's caring instinct is frustrated, and may even fail to develop. In extreme cases the mother will feel helpless and resort to an abnormal coping style. If nothing is done to prevent it this can start off a negative circle of persistently damaging relationships. These observations carry weight, since measures can be taken to prevent atopy and neuroticism.
The vicious circle of a damaging development can be prevented by intervening in the somatic as well as in the emotional-behavioural part of it. Atopy in infants has been prevented by anticipating its development. One should be prepared for allergy for cow's milk or egg-proteins in any pregnancy where the father or mother is known to have an atopic constitution. Controlled trials have shown the favourable effect of giving the baby enough time to develop his own immune competence while under the protection of the immune globulines from his mother's breast feeding. When both parents are atopic the child is likely to have a strong genetic tendency towards atopy. In that case the mother will do well to refrain completely from taking in egg- and cow's milk proteins, as their constituents may pass the placental barrier and sensitise the baby. Once the child is sensitised it is unlikely that the over-reactivity can be reduced unless an allergen-free diet is observed for a considerable time, after which a very careful and gradual re-exposure to the antigen may be attempted.
The neural analogy to immune competence is resistance to traumatic life events, including the skills to cope with daily life. Earlier in this paragraph we have used the term stress-immunisation. The term has originally been used by Poser for a form of treatment in adult psychiatric patients. Stress-immunisation as used in the present context is the habituation to and successful handling of stressful events in the every life of a normal child. It is more than habituation, it is learning to cope with stress. We have mentioned the example of separation. If a child has been separated from it's mother for short periods only, always having been reassured by her immediate reappearance on it's calling or crying for her, it will tolerate gradually longer periods of separation. It has learned to cope by anticipating her return. A child on the contrary who has felt betrayed on one or more occasions and has suffered a great deal of anxiety and desolation, may have lost his basic trust. He can feel lost and forlorn on the slightest provocation and resort to agonism: fight, flight or withdrawal. It may then be hard to reestablish a bond of basic trust.
The condition is even more difficult in the case of pseudo-tolerance to stress. There is cause for alarm when a child does not seem to notice or is indifferent to situations which seem threatening or dangerous to most other children. Not only are stress signals ignored, but the appropriate response: crying, an appeal for help, signs of distress, cannot be provoked. If such is the case, the normal circuit of emergency-responses has failed to develop, a neuronal development, that can be compared to pseudo-tolerance in the lymphoid network. The internal image of the self in relation to the environment is profoundly disturbed.
We assume that in a number of cases of childhood autism the normal process of stress immunisation has not taken place. The child, for want of normal coping skills, has regressed to abnormal lines of resistance around his vulnerable self. Do not hear, do not see, do not speak, and one can live in comparative safety. We have seen syndromes of abnormal withdrawal, sometimes with traits of autism, in sensorially or physically impaired children. Instead of a regression to a more primitive line of defence we have seen an inhibition or arrest of growth of personality spheres that are needed for developing speech and language. Therefore the study of language retardation includes the study of early learning and emotional growth.
Since the language system has a hierarchical organisation (9.10), it seems plausible that the functions relating to language also display the regression phenomenon. It can be illustrated by an example. When a badly wanted goal cannot be attained by cultured verbal behaviour, based on logic and polite persuasion, regression may occur to more primitive levels of oral communication. Depending on the circumstances it may take the form of less civilized language, inarticulate shouting, violent and frustrated crying, or weeping in helpless, appealing submission. Referring to figure 9.10.2 we see that during an agonistic outburst the mode of communication has regressed from the verbal levels 4-6 to the almost entirely pre-verbal levels 1-3.
The language system too may become conditioned to a regressive development. Cluttering is an example. Be it by attentional deficit, by lack of confidence, or by lack of temporal or spatial orientation, the person who is repeatedly frustrated in his communicative goals will give up further attempts to improve his verbal achievements. If left untreated, he will remain at a habitually primitive level of oral communication, deficient at the phonemic, the syntax or the logic level.
The lymphoid and the neuronal systems are neighbours in the time-window. Systems with response times that are not far apart interact with each other, and we can expect them to do so. The interfacing of the lymphoid and neural systems is self-evident to any unprejudiced observer. It has been obscured by the fact that lung- and skin-specialists have been more captivated by chemistry than by behaviour science. The contingencies of behavioural and allergic symptoms has not remained unnoticed, but has only led to a host of publications explaining the phenomenon as the result of allergic encephalitis, a very clumsy hypothesis. The recent upsurge of psycho-neuro-immunology as a new discipline was as predictable as the appearance of desert flowers after a shower. Experts in this field collect evidence that learning processes in the lymphoid and neuronal systems mutually influence each other. One could hardly expect otherwise: the systems are each other's environment, and as such in the best position to develop conditioned stimuli in relation to each other. At the end of this chapter I summarise briefly and I'll add to the example of the previous paragraph another one in which mutual conditioning has led to verifiable consequences.
A baby of a few months old has been left unattended for extended periods of time. Long periods of crying without response from the environment result in apathy and a psychological crisis. The result is periods of immuno-suppression, with an increased chance of relative overstimulation by antigens with which he has not yet learned to cope. As a result the antigen is not met properly by the first line of defence (by lack of a differentiated antibody response), it penetrates into primitive defence lines and causes inflammation. Since the antigen has not been recognised and properly coped with it gives rise to inflammatory reactions on subsequent occasions. As an allergen it gives rise to a skin rash or bronchial wheezing. The distressing consequences have been described in 6.5.3. The flow of events is depicted in Maps 6.6.1 - 3. It is clear that a vicious circle can be brought into motion at any point. As it is self-perpetuating, considerable effort is needed to bring it to a stop.
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