Page:Popular Science Monthly Volume 7.djvu/57

Rh thought for the thoughtful of all limes. Gradually these thoughts have taken form, and a science of psychology has grown up, engaging in its investigations the efforts of the ablest minds.

It may not be reasonable to suppose that any being, unless it be the Infinite, should perfectly comprehend itself. How far man is from being able to claim such knowledge may be inferred when we consider that, although he has been upon the earth so many thousand years, it is less than three centuries since he began to understand even his physical organization, or comprehend such simple facts in his own physiology as the process of digestion and the circulation of the blood. It is only within the present century that the functions of the nervous system began to be understood, and only within the last few years that its relations to mental activity have been intelligently studied. With so many points in regard to the functions of the material body only recently understood, and even now but imperfectly known, is it strange that our psychical relations should be even less perfectly comprehended?

A recent writer has pointed out the fact that each epoch of intellectual activity and enlargement, as marked by the discovery of new truths in Nature, has been accompanied or directly followed by better modes of investigation and more scientific views in psychology; and not only so, but the methods employed and the results obtained in psychology have had direct relation to the methods and results in physical science. As mathematics and the laws of motion gave us Descartes and Hobbes, scientific medicine or the "science of observation" Locke, the vibratory theory Hartley, and chemistry the elder Mill, so geology and the doctrine of evolution have been potent in influencing the methods and results obtained in psychology by Bain and Herbert Spencer. And as each advance in psychology has had reference to the methods in physical science which have preceded it, so do we find that the doctrine of evolution, which in its general aspect at least has given direction to the scientific thought of the present generation, has also been the doctrine which has thrown most light upon the constitution and action of mind.

It is not the object of this paper to discuss the doctrine of evolution, but simply in the light of that doctrine, as generally understood, to present such facts as science has prepared for us relative to the development of mind, and its manifesting organs in the gradually-ascending series of animal forms.

The organ of all psychical manifestation is the nervous system, and the material of which it is composed is substantially the same, whether in animals of a high or a low organization. It is of two kinds, the gray matter, usually found in nodules or masses of greater or less bulk, called ganglia, and the white matter, usually found in