The nervous system is composed of myriads of nerve cells, and of nervous fibres, which are long and exceedingly slender processes of these cells formed of similar substance, each shielded and insulated by a double coat. The nerve cells and the nerves are arranged in an ordered plan which has been unravelled by ingenious methods. They connect all parts of the body one with another. Think of the whole telephone system of Britain linked up together with millions of receivers, thousands of local exchanges, hundreds of central exchanges, etc., the nervous system with its sense organs, sensory nerves, lower and higher nerve centres and motor nerves, is infinitely more intricate than that. The whole forms an interlacing feltwork formed of watery nerve cells and processes, and not only receives sensory stimuli and transmits them as motor impulses, but is more or less permanently _modified_ by each sensory thrill which enters it, memorising each, more or less, for longer or shorter time according to its character or intensity. Thus the response of the nervous system to sensory excitation changes with education, habits form and character develops from birth to manhood, to decay again from manhood to old age, ceaselessly changing, but becoming graved on a certain plan. The making thereof depends on inborn qualities of the living substance--the conjugate product of the male and female parents, this moulded by environmental conditions, both in utero and after birth, by food, and the ceaseless instreaming of sensations. Depending on the nutrition of the cortex of the great brain, abrogated by narcotics, absent in sleep, consciousness of our being flickers from moment to moment, the product of the instreaming of sensations from the outer world and from our own body, and of memories of past sensations, aroused, by some present sensation. Conscious judgement arises from the balancing of present sensations with memorised sensations and leads to purposeful actions. Beneath the conscious world an infinite host of functions are carried out unconsciously, functions depending on the nervous connection of one part with another, just as the common people carry out a host of actions through the telephone system without the cognisance of the government which is seated at the highest central exchange. To find food, satisfy the sexual instinct, escape enemies, gain shelter from excessive physical changes of environment, the special senses and nervous system have then been evolved and perfected in the intricacy of their mechanism through vast aeons of evolution. There is evidence that man has for some million years trod the earth; but the senses of sight, hearing, smell, taste, touch were evolved in the vast procession of lower animals which preceded him for those millions of years which reach back and ever back to the first generation of life.