In its most extreme form behaviourism ex cludes everything which cannot be stated in the terms of organic response. This would still be ambiguous if the term organic were not taken to mean exclusively nerves, muscles and glands. In its most general terms the psychology of the behaviourists may be called the study of the stimulus-response situation. But while the terms stimulus and response define the field of observation, they must be limited in their application if behaviourism is to be given its exact significance. In the earlier period, before the theory reached its most extreme form, the main dispute was between the structural and functional views of psychology. The structuralist worked with elements and mental states which were described as complexes of elements. The functionalist did away with elements and substituted processes as forms of organic adjustment to the environment. One party was concerned with saying what the mind is : the other considered only what it does. The functionalist was influenced by the growth of biology and so came to use the term behaviour as the most convenient way of suggesting that the subject of his study was the life of the mind. By these gradual transitions a large number of psychologists became virtually be haviourists even before the school was conscious of its own stand ing. For example William McDougall in 1912 published a book with the title Psychology: the study of Behaviour, and defined psychology "as the positive science of the behaviour of living things." But the mark of this kind of behaviour is "the mani festation of purpose or the striving to achieve an end." In other works McDougall has defended animism (Body and Mind: A History and Defence of Animism) and continued to uphold a psychology based on the idea of purposive striving (Outline of Psychology 1923). Although the terms soul and mind and con sciousness are rejected as unsatisfactory, there is nothing in this form of psychology to offend supporters of the older tradition. But in the year 1913 John B. Watson put out the first statement of a more radical doctrine of which the essential feature was that all reference to consciousness should be condemned as unscientific. In 1914 Watson published the book called Behavior and in 1919 another book called Psychology from the standpoint of a Be haviorist. These works constituted the manifesto of the new school. It will be useful to note some of the tendencies which ex plain its appearance. As early as 1887 Carl Georg Lange produced a famous monograph on the emotions (Uber Gemiithsbewegun gen). In 1890 James restated a similar theory of emotions which he had partly outlined in 1884. The peculiarity of the theory consisted in resolving the emotion into the perception of the bodily changes which take place at the same time as the perception of the object sa;d to cause the emotion. The real emotion is the motor and other processes which occur in the body, as in flight or weeping, and qualify the state of cognition. Physiologists had already established the fact that the vasomotor disturbances (dila tation and contraction of blood vessels) were controlled by the sympathetic system and, though not voluntary, were functionally connected with the cerebral centres. The increasing recognition of this involuntary system and its activities encouraged those who were already inclined to write psychology in purely objective language. The most influential work came from Russia where Setschenow began as early as 1863 to say that psychology must take simple reflexes as its basis. The simple reflex would not have enabled psychologists to advance very far, but of ter the publica tion of the work of Pavlov on the salivary glands the idea of con ditioned reflexes became an important supplement. A reflex is said to be conditioned if a reflex action normally excited by a stimulus of one kind can be excited by another stimulus through associa tion. For example, if the flow of saliva due to the presence of food comes to be produced by ringing a bell, the reflex action of the salivary gland is said to be conditioned. After 1909 this became the stock example of mechanistic theories and supported the doctrine that behaviour is never more than a very complex set of conditioned reflexes. The knowledge of glandular action and par ticularly the ductless glands (endocrinology) was the new element in physiology and was also accepted as a new chapter in psychol ogy. One of the most influential books of this period was W. M. Cannon's Bodily Changes in Pain, Hunger, Fear and Rage (1915), which supplied more detailed facts about the physiological element in emotional behaviour, especially the automatic increase in the production of adrenalin under conditions of emotional excitement. The results seemed so much more scientific and exact than the other views on mental states that Behaviourism was advocated as the only scientific form of psychology. Carried out on rigidly theoretical lines, the principles of Behaviourism require the psy chologist to avoid all such terms as sensation, emotion, memory or thought. Sensation is neural response : emotion is glandular or visceral response : memory is neural habit : thought is verbalized response or language behaviour. This theory has the advantage of being apparently simple and using only objective terms. It has the disadvantage of being paradoxical and failing to do more than state the bodily functions in which mental states are objectified. (See BEHAVIOURISM.) Animal Psychology.—The attitude of the behaviourist has been due in large part to the progress of Animal Psychology. This has been compelled to rely on objective data and either ignore or deny any factor called consciousness. Animal behaviour is an ancient study which belongs primarily to zoology. It became a part of psychology after the work of Darwin had shown the im portance of studying human and animal behaviour comparatively. A large amount of material had been collected by various writers from Aristotle and Pliny to C. G. Leroy and Reimarus in the eighteenth century. Leroy especially was a good observer and earned commendations from Darwin. Some, like Descartes, classi fied animals as machines; a view revived and supported by T. H. Huxley. Others retained a more generous view with an inclina tion to be sentimental and anthropomorphic. The idea of con tinuity in human and animal life was deeply resented by orthodox thinkers, and the shock of this resentment was largely borne by G. J. Romanes. He wrote on Mental Evolution (1878), Animal
Intelligence (1882) , Mental Evolution in Animals (1883 ) , Mental Evolution in Man (1883). This epoch was mainly descriptive : it passed away when the problems of animal behaviour were taken into the laboratory. In 1890 Jacques Loeb published a work on Der Heliotropismus der Tiere, followed by another Uber die Bedeutung der Tropismen fur die Tierpsychologie and Studies of General Physiology (1905). This work was primarily physiological. Loeb made popular the term tropism, a form of behaviour which consists in "turning" from one position to another as a result of unequal stimulation. The term was in use in the case of plants (heliotrope) which "turn" to the light in the sense that light stimulates the kind of cell growth which results in that position. Loeb was prepared to explain the behaviour of the moth when it flies into the flame by a similar analysis. The physicochemical changes would then be the only factors needed to explain animal behaviour. The truth of Loeb's thesis is not open to dispute in particular cases, but it is not possible to make it adequate for all cases without too free use of the imagination. The physiological method requires to be supplemented by the biological. In this direction very important work was done b.y Lloyd Morgan, Intro duction to Comparative Psychology (1893), Instinct and Habit (1896) and other works. The mechanistic school was represented by Bethe, Uexkiill, Ziegler and others in Germany. In 1904 H. S. Jennings published the results of his experimental work in a volume entitled Contributions to the study of the Behavior of Lower Organisms. The phrase "trial and error" was made cur rent by its use in this connection. The experimental work be gun by Jennings on lower organisms has been carried on in a great variety of forms by many workers, especially in America. A pioneer in the work was E. L. Thorndike (Animal Intelligence, 1898), followed by Yerkes, Parker, Holmes and others. In France G. Bohn published La Naissance de l'Intelligence (1909) and La Nouvelle Psychologie Animale (1 91 0). These are only samples of a great variety of contributions which range from the amoeba and ants to the chimpanzee. One of the most important points for the psychologist is the question of learning. The experimental work has largely been devoted to the problems of the learning process. The maze has been most extensively used for this purpose, and other contrivances such as the box with the closed door which the animal must open to get its food. While the progress has been cumulative and valuable, the methods have not been very original or satisfactory. A new possibility was introduced by Wolfgang Kohler when he studied the apes in the German zoological station at Tenerife. Kohler devised problems which could not be solved by the blundering tactics of trial and error: the apes were compelled by the circumstances to use methods which involved more intricate mental processes. Kohler contends that the solution of the problem is reached by an act of insight, a grasp of the logical significance of the whole situation. If this is true the trial and error doctrine needs re vision, at least in the case of the higher animals. (See PSYCHOL OGY, COMPARATIVE.) Child Psychology.—Child psychology is the most modern of all departments of the subject. Though animal psychology has a long history, human psychology was consistently limited to the reason of the adult man instead of being treated genetically. It is a curious fact that no distinctive treatise on child-psychology appeared before Dieterich Tiedemann (1748-1803) wrote his Bookachtungen fiber die Entwickelung der Seelenfahigkeiten bei Kinder (1786). This work was translated for the Journal General de !Instruction in 1863, quoted by Perez in a book on Tiedemann in 1881 and translated into English in 1877 as A Record of an Infant's Life. In France Perez, Egger and Corn payre produced works of some importance. In America F. Tracy's book, The Psychology of Childhood (1893), had a wide influence and was later translated into several languages. Other works in the earlier period were produced by Lobisch (Entwicke lungsgeschichte der Seele des Kindes, 1851), by Sigismund (Kind and TV elt, 1856) and by Kussmaul (Untersuchungen weber das Seelenleben des neugeborenen Menschen (1859). The date of the last work coincides with the rise of Darwinism. Here as elsewhere Darwin was a pioneer, setting the example of keeping a daily record of a child's development. Taine imitated this example, but both essays were relatively small contributions, ap pearing as articles in Mind, 1877. A more ambitious attempt was made by Wilhelm Preyer, Die Seele des Kindes (1882), which reached a seventh edition in 1908. In 1895 Sully published his Studies of Childhood. Stanley Hall and Mark Baldwin also made notable contributions. The subject has since expanded into a large literature which is partly child-study, partly a division of genetic psychology and partly a product of educational psychol ogy. In Germany W. Stern published in 1914 a comprehensive work translated into English under the title Psychology of Early Childhood (1924). In its latest stage of development child-psy chology has become practically a study of human behaviour from birth onwards. The behaviourist is interested in the reactions of the infant, whether they can be defined as mental or not. Be haviour in this sense begins with the earliest reflexes, is observed and described according to the correlation with chronological age, and is explained chiefly in terms of conditioning. In this work John B. Watson has set an example and data are being continually supplied by other students. Educational psychology is concerned with children at the school age and aims to establish norms of achievement with a view to improved methods of training. Here the intelligence-tests play a large part and much experimental work is being done on subjects of instruction, such as reading, writing and arithmetic. The work of E. L. Thorndike in America (Educational Psychology, 1903) represents the historical basis of the work belonging to this branch of applied psychology. Among other contributions those of E. Meumann and E. Claparede de serve special mention.