"The Origin of Species" with its principle of natural selection, its preservation of useful qualities, the influence of environment and heredity, gave the genetic theory strong support. The views presented by its illustrious author were set forth with such clearness and defended with such wealth of illustration as to make their rejection a matter of great difficulty. Even those who were most hostile recognized their importance as well as their revolutionary character. It was evident to nearly every scientific man that henceforth the world could not be explained upon morphological theories alone, and that some such principle as that of natural selection must be presupposed in order to explain the facts which in almost every department of scientific research were daily coming to light. Natural selection has been defined as "that process in life, automatic in its nature and action by which in the struggle for existence useful differences are preserved and those which are not useful are destroyed." It is under the operation of this principle Spencer believed, and sought to show, that species are formed and the various manifestations of life accounted for. Those who accepted Mr. Spencer's theories in full, with few exceptions, accounted for the origin and evolution of the universe on purely mechanical principles.
But the questions as to life itself, its nature and its origin, were not on this evolutionary theory fully answered. Granting that the lowest forms of life are connected with the cell, that life is manifested in its structure and through its growth, even on the assumption that matter and energy only exist, the question can not be pushed aside. Whence is the energy which brings life into matter, organizes it and imparts to it the power or ability under the laws of evolution to create, perfect and continue at pleasure, the forms in which it chooses to appear? Logically the genetic theory must explain the origin and continuance of life on mechanical principles alone. A theory in sharp contrast to the genetic or evolutionary theory, which for many minds reduces life to a mechanical process, is what Mr. Merz calls the vitalistic theory. This theory is becoming more and more prominent with the increasing interest in the study of biology. What life is, what is its origin, what are its processes, are questions to which as yet completely satisfactory answers have not been returned. Bichot (1771-1802) defined life as the "totality of functions which resist death," a definition which gives little information as to the nature of life, or its origin. Claude Bernard (1813-78) wrote "life is the struggle of living forces against the non-living." Since the publication of Darwin's book on "The Origin of Species," or more exactly since 1866, a tendency is to be noted which seeks to establish parallelisms between processes in organic and inorganic bodies. Lavoisier was one of the first to study life from a chemical point of view, and to explain respiration, nutrition and the generation of animal heat as a form of combustion. In
