memory, instincts, intelligence and will; the continuity of consciousness is associated with the continuity of these activities, as well as with the structures of the body in general and of the brain in particular. It is well known that things which interrupt or destroy these functions or structures interrupt or destroy consciousness. Lack of oxygen, anesthetics, normal sleep cause in some way a temporary interruption of these functions and consequently temporary loss of consciousness; while certain injuries or diseases of the brain which bring about the destruction of certain centers or association tracts may cause permanent loss of consciousness.
The development of all of these psychical faculties runs parallel with the development of bodily structures and apparently the method of development in the two cases is similar, viz., progressive differentiation of complex and specialized structures and functions from relatively simple and generalized beginnings. Indeed the entire organism—structure and function body and mind—is a unity, and the only justification for dealing with these constituents of the organism as if they were separate entities, whether they be regarded in their adult condition or in the course of their development, is to be found in the increased convenience and effectiveness of such separate treatment.
Development, like many other vital phenomena, may be considered from several different points of view, such as (1) physico-chemical events involved, (2) physiological processes, (3) morphological characters, (4) ecological correlations and adaptations, (5) psychological phenomena, (6) social and moral developments. All of these phases of development are correlated, indeed they are parts of one general process, and a complete account of this process must include them all. General considerations may lead us to the belief that each of the succeeding aspects of development named above may be causally explained in terms of the preceding ones, and hence all be reducible to physics and chemistry. But this is not now demonstrable and may not be true. Function and structure may be related causally, or they may be two aspects of one substance. The same is true of body and mind or of matter and energy. But even if each of these different phases in the development of personality may not be causally explained by the preceding ones, at least the principle of explanation employed for any aspect of development ought to be consistent and harmonious with that employed for any other aspect.
The phenomena of mental development in man and other animals may be summarized in the following table:
Development of Psychical Processes in Ontogeny and Phylogeny
| All Living Things, including Germ Cells and Embryos, show: | Mature Forms of Higher Animals show: | |
| 1. Differential Sensitivity = | 1. Special Senses and Sensations = | |
| Different Responses to Stimuli differing in Kind or Quantity. | Sensations are the Elements of Mind. |
