Page:Popular Science Monthly Volume 7.djvu/68

58 take in the idea of "quantitive reasoning" nor "correlation of forces." The dog is capable of improvement, limited only by his organization; the Hottentot only by his, and the child, of a large-brained and cultivated ancestry by his. The difference in these possibilities, however, can only be comprehended upon reflection. The most intelligent animal, or even the savage man, bears relations to no surroundings beyond the mere seeming of things upon the few acres or miles traversed by his race or tribe; the sun and moon are only what they appear; they rise just beyond the mountain, and they go down in the forest. The thunder and the tempest are incomprehensible, or are the voice and breathings of an angry God. The philosopher, or man of science, on the contrary, holds converse with all objects, animate and inanimate; all peoples and their works, both present and past, upon the surface of the earth. He explores its depths, and calls up before him the generations which peopled it ages on ages past. The microscope brings before him the world of the infinitely small, and the telescope reveals the worlds of space. With the spectroscope he questions the stars, and they give intelligible reply. Such, and a thousand-fold more, are his surroundings; and it is to express his relations to these, to the complex impressions and sensations to which they give rise, and the reflections and aspirations which they inspire, that the brain of the philosopher must be adequate.

We have thus noticed the more prominent structural changes as they occur in the nervous system, from its simplest form to its highest development, and also the corresponding psychical manifestations, which each advance in structure rendered possible. We have seen the lowly creature, endowed with its single nerve-centre, and its radiating nerve-filaments, expressing all its relations to the outer world by simple reflex action; and, if, as we should expect, the order of appearance in Nature corresponded with the order of development, for untold ages all over the silent, ocean-clothed earth, no higher form of life, and no higher expression of soul, was present. Gradually, by many a minute addition, in response to improved surroundings and new requirements, new organs appeared, until at length there existed a creature of definite form, with organs of sight and hearing, as well as touch and locomotion. The old ganglionic nerve-system, with its simple reflex movements, was still retained; but, to express the many new relations to the outer world which its gradually-acquired organs made possible, additional nerve-centres were required, and the sensorium assumed form and use. The series of actions performed through its promptings we call instinctive. Then for unknown ages sense impressions, stimulating to instinctive action, were the highest expressions of soul upon the slowly-emerging earth.

But, again, improved surroundings—the dry earth, with forest, field, and flower, the brighter sunlight and the purer air, demanded new organs to appropriate and new senses to enjoy; and a race