MODERN science has so extended the horizon of our mental perspective, has achieved such brilliant triumphs in so many departments of thought, and, on the basis of verified fact, has erected such an imposing superstructure of useful knowledge in the domain of inorganic nature, that some, rejecting the vitalistic theories of the past, have accepted the belief that the deeper mysteries of vital phenomena will, in a final analysis, be demonstrated to be but resultants of physical forces acting under the complex conditions of organization.
To investigate and interpret the varied phenomena of nature is the unquestioned prerogative of the human intellect; but science, having to do only with "particular orders of phenomena which exist in relation to the percipient mind" and are susceptible of verification, does not hope to solve the profound mysteries involved in the ultimate realities of either matter, energy, or life. With restless energy the human mind presses on in its search for truth, and brings from varied sources new facts to add to the sum of knowledge, until the conclusion is reached that matter is indestructible and energy persistent, and in the formulated laws of the "correlation and conservation of energy" the widest generalizations are made. In thus classifying and uniting the manifestations of matter and of life, whether morphological or physiological, under one general cosmic law, their explanation is made complete within the limits of the known.
Phenomena are explained, but the absolute remains unrevealed. The questions still are asked: What is gravity? What are chemical, electrical, and vital forces? What is the essential nature of matter, energy, and life? There is no oracle to answer.
The study of vital phenomena is difficult because of their complex character, and, in the absence of exact analysis, speculative philosophy has for many ages ventured different theories in explanation of their nature. In seeking to give the present status of physiological science on this important question, it is of interest to take a general historical retrospect, in order that the steps of progress may be observed.
The atomic philosophy, as taught by Democritus and Epicurus, recognized but one kind of matter, whose elements, by virtue of their various forms, had the property of diversified and endless combinations. This play of atoms, independent of an overruling intelligence, produced the worlds of inorganic and of organized matter, which move on in endless cycles and are obedient only to physical forces.
Plato regarded the intelligent soul as of dual character: one part, located in the body, being mortal and presiding over the appetites and