Comparative Psychology seeks the genealogy and genesis of mental phenomena. It recognizes that between mind and body there exists an intimate relation. We may, therefore, address ourselves first to that branch of it which connects most directly with the physical sciences, – to Neurology. We must notice: the structural unit of the nervous system, – the neuron; the representation of parts of the body in the nervous system; kinesodic and æsthesodic centres and systems; the functions of the nervous system in general; the nutritive property of centrifugal nerves. All our knowledge points to the interdependence of mind and brain. Does the brain grow after the individual has reached maturity? Certain parts of the proliferating epithelium persist late, and continue to form cells. How long does this go on, and what are the conditions of the proliferation of new nerve cells? The migrations, development, and successive modifications of the (ultimately) brain cells are of great practical importance. Cf. the cerebellum, an organ without psychical significance, but serving as a "reservoir of nervous energy, which backs up the feeble mandates of the will." Not only the origin, but the subsequent nutrition of nerve centres is an interesting problem. We must look to the lymph and to auxiliary cells for an explanation. An overdraft on the proliferating power may permanently limit the sources of future nervous supply. Moderate mental activity is essential to cell-multiplication. Senile degeneration may be due to loss of nerve power, dependent on exhaustion of the proliferating centres. This latter is an important problem. Through the organic sensations, neurologically considered, we may hope to study the emotions. Neurology, then, throws light on the subjects of health, persistence of mental power, and on the problems of Psychology itself.
After a preface defending experimental psychology against the charge that its results are fragmentary and without bearing on the general problems of mind; and an introduction emphasizing the importance to physiology, psychology, and sociology of a study of the development of will; the writer contributes towards such a study
