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*The Problem of Seeing.*—What we call seeing is vastly more than the stimulation of the brain through the action of light upon afferent neurons. It is the perceiving of all the different things that make up our surroundings. If one looks toward the clear sky, he receives a sensation of light, but sees no object.
*Sense Organs.*—The sense organs are not parts of the afferent neurons, but are structures of various kinds, in which the neurons terminate. Their function is to enable the sensation stimuli to start the impulses. By directing, concentrating, or controlling the stimuli, the sense organs enable them to act to the best advantage upon the neurons.
Apart from Change there is no reality. Images as data Nerves, afferent and efferent, cannot beget images, nor can the brain give rise to representations All our perception relative to action. Denial of this involves the fallacies of Idealism or of Realism Perception and knowledge Physiological data Zone of indetermination "Pure" perception Memory and Perception.
This explains how physical exercise increases the breathing, since the muscles at work consume more oxygen than when resting and give more carbon dioxide and other wastes to the blood. The respiratory center is also connected by afferent nerves with the mucous membrane of the air passages.
At once this sensation is telegraphed over the afferent nerves to the nerve centers in the brain or spinal cord. In response to this call of distress the command comes back over the efferent nerve filaments: "Withdraw the fingers!" At the same time the impulse to withdraw the fingers is sent over the motor nerves to the muscles and ligaments which control the movements of the hand.
It is now our purpose to consider the effect produced by afferent impulses upon the brain and, through the brain, upon the mind. This effect is manifested in a variety of similar forms, known as *The Sensations.*—Sensations constitute the lowest forms of mental activity. Roughly speaking, they are the states of mind experienced as the direct result of impulses reaching the brain.
Further, the great mass of seemingly-voluntary acts in such creatures as insects, worms, molluscs, are considered by physiologists to be as purely automatic as is the dilatation or closure of the iris under variations in quantity of light; and similarly exemplify the law, that an impression on the end of an afferent nerve is conveyed to some ganglionic centre, and is thence usually reflected along an efferent nerve to one or more muscles which it causes to contract.
Locate and give the approximate number of the sympathetic ganglia. Show how the two portions of the spinal nerves are formed—the one from the mon-axonic and the other from the di-axonic neurons. Enumerate the different agencies through which the brain and spinal cord are protected. What cranial nerves contain afferent fibers? What ones contain efferent fibers?
But in sleep the exciting influence of the brain is diminished, and the brain transmits much less of the normal excitement and normal tension to the spinal axis with its ramifications in the afferent and efferent nerves; in the waking state an external impression is promptly conveyed to the centres, whence it returns in corresponding movements with the usual connection and rapidity, whether reflex or deliberate.
They are acted upon by external stimuli, while their impulses in turn act on the neurons in the spinal cord. This, the intermediate division, may be composed of mon-axonic neurons, or it may consist of branches from the afferent neurons. From the central nervous system to the muscles. This, the efferent division, is made up of mon-axonic neurons.
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