The dominant medical model of Western culture, the biomedical model, is based on three underlying, yet untested, assumptions and principles: (1) objectivism, the idea that accurate knowledge can be exclusively achieved through an impersonal assessment of sensory based information; (2) determinism, the idea that causation is exclusively characterized by an upward and linear mechanistic linkage; and (3) positivism, the idea that knowledge exclusively accumulates through the accretion of data from the positive results of sensory based experimentation. This model has served us well, but with the progressive urbanization of life accompanied by the industrial and technologic revolutions humankind has seen the development of new and very different adversities, which have resulted in the emergence of a uniquely new category of modern day ailments, particularly stress related diseases, acute and chronic that are directly linked to personal attitudes and lifestyle. As a result, the limitations of a medical model that cannot effectively incorporate psychological, psychosocial, or spiritual factors-factors that are at the source of these ailments-has become increasingly evident.

The emerging public interest in health promotion, self-care, alternative healing practices, and mind/body medicine is a response to the limitations of the biomedical model and challenges future health practitioners to develop a more comprehensive understanding and approach to the care of individuals (Eisenberg et al., 1993). Ideally, such an approach would maintain the scientific rigor and discipline that has so successfully served the biomedical model while at the same time expand the vision and reach of modern medicine. New approaches to clinical care must be developed in a manner that can be easily integrated into clinical training and effectively assist the future practitioner in meaningfully expanding his or her capacity to respond to the changing needs and demands of a diverse population of clients.

The comprehensive model proposed here incorporates and integrates the principles and practices of the biomedical model with the new and emerging initiatives noted above. It does so by presupposing that there are multiple maps and explanatory models for perceived reality. Each map is considered valid in itself, yet when considered together they provide a closer approximation to reality than is possible when each is taken alone. As complex beings living in a complex ecology, we can appropriately and simultaneously be considered as instinctual beings whose systems are amenable to repair, interactive units whose major component systems are the mind and body, and spiritual beings who emerge from and ultimately rejoin the timeless flow of nature. The model I am proposing will consider each of these aspects of our being-instinctual, mind/ body, and spiritual-their relationship to each other, and the manner in which each can be integrated into a comprehensive approach to health.

This approach will be based on new set of assumptions and principles which incorporate, yet expand upon, those of the biomedical model. The first principle, dynamism, reflects the view that the human experience is at all times in an active and vital relationship with its environment, continuously exchanging nutrients and information and adapting to new and different circumstances. Unlike a machine that cannot change itself once it is set in motion, humans can repair their own tissues, regenerate new tissue, and through will adapt to varying external conditions by altering their actions. The second principle, holism, is the term that we use to designate the viewpoint that human life is a natural, self-organized, unfolding process that consists of constituent elements bound together from the very beginning as a unitary interactive whole. If an embryo is homogenized into a soup that contains all of its initial ingredients (DNA, RNA, and so forth) it is not possible to reconstitute a living embryo from these isolated parts. The memory and pattern of the whole precedes the development of the parts and is disrupted when the intact living process is altered. The final principle, purposefulness, intentionality and goal directed activity, can be found at every level of the human experience: The automatic mechanisms of homeostasis are directed towards maintaining a precise physiologic balance; the in-born psychic instincts, the Jungian archetypes, outline the patterns, intentions, and directions of psychologic development which sustain a continuity and stability of the human experience; and consciousness appears to follow the universal quest to expand itself sufficiently to understand and re-unite with the ground of its being. Together, these three principles extend our understanding of the human condition and recognize the full range of healing capacities built into the human mind and body.

Systems Theory
Based on these new assumptions and principles, the model I am proposing draws upon the knowledge of systems theory that first developed as a modern response to the accumulation of expanding volumes of information and data and an increasing emphasis on microspecialization. Systems, or organizational theory, is an attempt to integrate, to create wholes out of parts. It is in essence a science of wholeness. Its concepts and principles are based on the observation that nature is organized in patterns of increasing complexity and comprehensiveness, and that these larger wholes, or units, have characteristics and qualities unique to the whole and cannot be identified or accessed through an analysis of their component parts (Weiss 1977; van Bertalanffy 1968). For example, the human organism, composed of cells, tissues, and organ systems, contains qualities and characteristics that cannot be exclusively accounted for through the linear summation of its parts. These include the capacity for self-organization, integrated action and adaptability, will, intention, and creativity.

In the 1970s George Engel, using the principles of systems theory, developed the biopsychosocial model, an expanded model of healing (Engel 1980, 1982). His intent was to extend the biomedical model to include the psychologic and psychosocial factors that are largely excluded from it. The model I am proposing similarly draws upon systems theory, but unlike Engel's biopsychosocial model, which is based on the biosocial hierarchy of nature, the health continuum is based on a hierarchy of healing systems, which are seen as the essential linkage between cellular physiology and social adaptability. The model is composed of four healing systems: homeostasis, treatment, mind/body, and spiritual. Figure 1 illustrates the relationship of the component parts to the whole.

Fig. 1. The health continuum.

Each of the subsystems of this model is a complete and distinct whole in itself, yet at the same time it is part of a more comprehensive healing system. As an intact system, each of these component systems has its own frame of reference, operating principles, internal stability, characteristics, and research methodology. As we ascend the hierarchy of healing systems we expand our conceptualization of healing, adding both complexity and comprehensiveness at each new level. Each component of the systems can be studied separately, and the entire system can be studied both in terms of its system wide characteristics and the interrelationships of its component parts. For the scientific researcher, it is appropriate to selectively study a particular system applying the research methodology appropriate to the system under study. The practitioner, however, whose focus is always the whole person, must have the dual concern of attending to the individual components of the healing system while simultaneously considering these components within the context of a more inclusive and comprehensive multisystem approach to healing.

System 1: The homeostatic healing system
Walter Cannon described the most primary and basic healing system available to the human organism, the homeostatic system (Fig. 2). This built-in instinctual system of internal physiologic checks and balances evolved over the millennia of human development, providing the human organism with the potential to automatically respond to internal states of disequilibrium with immediate, reflex like physiologic corrections. This system assures the maintenance of a steady physiologic state, which in turn ensures survival.

However, our homeostatic system is far more suited to the life of primitive humans than it is to the more recent and dramatic changes in lifestyle and environment that characterize and accompany "civilized" urban life (Williams and Neese 1991). As a consequence, the homeostatic system is often maladapted to the changing lifestyles, practices, and environments of modern humans: our nutritional choices, exercise patterns, physical environments, and above all our stress levels. This mismatch of primitive adaptive mechanisms and the realities of modern life have resulted in significant limitations and deficiencies in the natural protective mechanisms designed into this system. For example, the maintenance of normal glucose levels and the integrity of our vasculature is undermined by our modern day diet and sedentary lifestyle, and the on and off mechanism of the stress response and the maintenance of normal levels of blood pressure are distorted by the presence of unrelenting mental stress. To remedy the results of the mismatch between the built-in mechanisms of the homeostatic healing system and the realities of urban life civilized man has developed "treatment" models whose purpose is to step-in where homeostasis has failed and to restore normal function.

System 2: The treatment heating system
The treatment system is activated when the patient seeks assistance from a health-care practitioner as a reaction to the appearance of a symptom or the presence of overt disease, an indication of the breakdown of the natural homeostatic system. This is routinely followed by the requisite testing, establishment of a diagnosis, and the prescription of therapy, usually, in the biomedical treatment system, in the form of external agents such as drugs, surgery, or physical therapy (Fig. 2). Biomedicine, the dominant form of treatment in western society, seeks to establish and explain causation by reducing the field of study to a single body system and its associated biochemistry. Its aim is to repair the biophysiologic abnormality and re-establish health, which in the biomedical system is defined as the restoration of normal function.