Nothing is known to us until it has been transmitted to the mind by the senses. The nerves of special sense, of sight, hearing, smell, taste, touch, the temperature sense (“hot or cold” sense), the muscular sense (sense of weight and position), these, and the nerves controlling voluntary motion, form the peripheral, or surface, nervous system. This acts as a connecting medium between the outside world and the central nervous system, which is composed of the brain and spinal cord. We might liken the nerves, singly, to wires, and all of them together to a system of wires. The things of the external world tap at the switchboard by using the organs of special sense; the nerves, acting as wires, transmit their messages; at the switchboard is the operator—consciousness—accepting and interpreting the jangle of calls.

The recognition by the brain of the appeals coming by way of the transmitting sense, and its interpretation of these appeals, is the mind’s function of consciousness, whether expressed by thinking, feeling, or willing.

The Central and Peripheral Nervous Systems in Action

I am passing the open door of a bake-shop, and a pervading odor fills the air. I think “hot rolls,” because my organ of smell—the nose—has received a stimulus which it transmits along my olfactory nerves to the brain; and there the odor is given a name—“hot rolls.” The recognition of the stimulus as an odor and of that odor as “hot rolls” is consciousness in the form of thinking. But the odor arouses desire to eat—hunger; and this is consciousness in the form of feeling. The something which makes me walk into the shop and buy the rolls is consciousness in the form of willing. The sensory appeal from the outside world gained admission through the sense of smell; this transmitted the message, and consciousness recognized the stimulus, which immediately appealed to my hunger and incited action to satisfy that hunger.

The ear of the operator in the telegraph office, again, might illustrate consciousness. It must be able to interpret mere clickings into terms of sense. To the operator the sounds say words, and the words are the expression of the object at the other end of the wire. The brain is the receiving operator for all the senses, which bring their messages in code, and which it interprets first as sound, vision, taste, touch, feel, smell, temperature; then more accurately as words, trees, sweet, soft, round, acrid, hot.

The mind can know nothing except as the stimulus is transmitted by sense-channels over the nerves of sense, and received by a conscious brain. A baby born without sight, hearing, taste, smell, or touch would remain a mere bit of clay. He could have no awareness. But so long as any one sense channel remains open the mind may acquire some knowledge.

Suppose I am paralyzed, blind, and deaf, and you put a tennis-ball into my hand. I cannot tell you what it is, not even what it is like. It means nothing whatever to me, for the sense channels of touch, sight, and hearing, through which alone it could be impressed upon my brain, are gone. Suppose I am blind and deaf, but have my sense of touch intact; that I never saw or touched or heard of a tennis-ball before, but I know “apple” and “orange.” I can judge that the object is round, that it is about the size of a small orange or apple. It is very light, and has a feel of cloth. I know it to be something new in my experience. You tell me in the language of touch that it is “tennis-ball”; and thereafter I recognize it by its combination of size, feel, and weight, and can soon name it as quickly as you, who see it.

Suppose I am blind and my hands are paralyzed, but I have my hearing. You tell me this is a tennis-ball, and if I have known “tennis-ball” in the past, I can describe it to you. It has been impressed upon my brain through my sense of hearing; and memory immediately supplies the qualities that go with “tennis-ball.”

But if none of the senses has ever developed, my brain can receive no impression whatever; it cannot have even the stimulus of memory. Hence conscious mind cannot be, except as some sense-channel or channels have been opened to carry thought material to the brain. So far as we know today, in this world, mind is absolutely dependent upon the sense organs and the brain—upon matter—for existence.

The Sympathetic Nervous System

Associated with the central nervous system by connecting nerves—but located outside of it in various parts of the body—are groups of nerve-cells (gray matter) and their fibers, forming what we call the sympathetic nervous system—the direct connecting link between mind and body.

The central nervous system is the director of all conscious action of the body; the sympathetic orders all unconscious action.

The beating of the heart, the contraction of the blood-vessels, hence the flowing of the blood, the processes of digestion, the functioning of the glands, are all directed by the sympathetic. In other words, the central nervous system normally controls the movements of the voluntary muscles; the sympathetic controls those of the involuntary muscles.

The quick blush, the sudden paling of the cheeks, the start of fear, the dilated pupils of fright are the direct result of the action of involuntary muscles under control of the sympathetic system. The stimulus is received by the central nervous system; the fibers connecting the central and the sympathetic systems carry the message quickly to the latter, which immediately respond by ordering contraction or expansion of involuntary muscles. So tears flow, we breathe freely again or we quake and tremble, our pupils widen or contract, the heart beats suffocatingly, or seems almost to stop.

The sympathetic system, as the name implies, is influenced by suggestions from the emotions rather than from the intellect. We might say that it is controlled by the “feeling mind” rather than the thinking mind, for intellect cannot influence it in the least.

The wise nurse, who knows something of the laws of the mind, soon realizes that the sympathetic nervous system, rather than physical disability, causes many indigestions, headaches, diarrheas, dry mouths, chills; is responsible for much nausea, much “exhaustion,” etc. When she has had wider experience she finds that almost any known physical disorder can be unconsciously imitated by the suggestible patient, whose sympathetic nervous system causes physical reactions to respond to the feelings of a sick mind. Let the nurse remember, however, that is it not for her to decide whether the disorders from which her patient suffers are of physical or nervous origin. It is for her, on the other hand, to study her patient’s mentality and reactions, and to become expert in reporting symptoms of nervous as well as of physical significance.