By the employment of psychotherapy we simply make use of the normal mechanisms of the physiological organism; we can do nothing more, we should do nothing less. "That ideas work on the lower centers of our central nervous system, and bring into renewed activity centers which regulate the actions of our muscles, blood vessels, and glands, must be accepted as the machinery of our physiological theory." 1 The connection of such theories with purely physical facts is given by our every-day processes of experience, and is evident to the most casual observer.

In his elucidation of the psychological principles and field of psychotherapy, presented before the American Therapeutic Society at the annual meeting in New Haven, Professor Morton Prince tells us: 2

"It is a law that associated ideas, feelings, emotions, sensations, movements, and visceral functions of whatever kind tend, after constant repetition or when accompanied by strong emotion of feeling tones, and under other conditions, to become linked together into a system or group in such fashion that the stimulation of one element of the group stimulates the activity of the rest of the group. Such a group is conveniently called a 'complex,' and I shall hereafter refer to it as such. This tendency to the linking of functions obtains, whether the mental and physiological processes when linked form a complex which subserves the well-being of the organism and adapts the individual to his environment, or whether they form one which does not subserve the well-being of the individual, but misadapts him to his environment. In the former case the complex is called normal; in the latter, abnormal. This is only another aspect of the well-accepted principle that pathological processes are normal processes functionating under altered conditions.

Both are the expression of one and the same mechanism."

Professor Prince further says:

"The linking of function may be almost entirely of ideas, as is expressed by the well-known psychological law of association of ideas. Its pathological manifestations we see in so-called fixed ideas or obsessions. We see it also exemplified within normal limits in so-called moods, when certain large systems of ideas, accompanied by strong emotion tones, occupy the mental field to the exclusion of other systems which find it difficult to take the possession of the field of consciousness. When such moods are developed and intensified to an extreme degree, we have veritable pathological alterations of personality, and even, it may be, multiple personality. But in moods besides association we meet with another principle in an exaggerated form - namely, dissociation.

1 Hugo Munsterherg.

2 Journal of Abnormal Psychology, June-July, 1909.

"The linking, again, may be of physiological processes, as exemplified by synergesis of muscular movements. This is seen in the linked combination of muscles used in writing, piano playing, and skilled use of tools and implements of games.

"Unless nervous processes could be artificially linked into coaptive synergistic systems adapted to a purpose, education in any field would be impossible. Intellectual acquisitions, from the repetition of the alphabet to a complete knowledge of a language or a science, and physiological acquisitions, from the use of a tool to the mastery of the piano or the vocal apparatus, would be not only unknown, but would be unthinkable. The education of the mind and body depends upon the artificial synthesizing of functions into a complex adapted to an end or useful purpose. By the same principle functions may be synthesized by education into a complex which does not serve a useful purpose, but rather is harmful to the individual. When this is the case, we call it abnormal or a psychoneurosis."

It is important to remember that psychic elements are correlated to the physiology of the brain just as physical processes are correlated to cerebral excitations. Physiological psychology deals with those psychical phenomena to which concomitant physiological processes of the brain correspond. Psychotherapy is but the application of well-demonstrated principles of physiological psychology for therapeutic purposes. It is not necessary for us to deduce from the conception of psychical life the possibility of applying mathematical computations to that field of science. Physiological psychology has, however, established important propositions capable of mathematical statement. We have become acquainted with a series of psychophysical laws; psychophysics has therefore become a component part of the science of psychotherapy. As physicians, we are interested only with that branch of empirical psychology designated as physiological psychology, which embraces the conception of psychical processes with concomitant cerebral processes.

We are at times confronted with the question, How do we recognize phenomena which we designate as psychical? All and only the phenomena which are imparted to our consciousness are psychical. That which is without us in space and time, which we assign as the cause of our sensations, is material. The object whose existence we accept as external to us when we have the visual sensation of the thing seen by the eyes is material. The sensation of sight itself is psychical in so far as it concerns our consciousness. Apparently "psychical" and "conscious" are wholly identical, for we can form no idea at all of what an unconscious sensation may be; but upon closer investigation we shall find that every conscious sensation has, at least to all but a few of us, an unconscious effect. Concomitant physical processes corresponding to the psychical processes, the process of experience, are conserved by neuron elements and become in the future a part of our personality. The more intense the psychical process, the more active is the functionating of the nervous mechanism conserving the experience.

Concomitant psychical processes appear and reappear, strengthened or weakened by similar experiences, in response to material excitations of the nervous mechanisms conserving such experiences. 1