will, in most cases, suspend the conductivity, but the functions promptly return upon warming. This is illustrated by freezing any part of the body, the chilled nerves not being able to conduct impulse, the part affected is said to have "no feeling." One feels the cold before reaching the freezing point, but when this is reached freezing occurs unconsciously.

The fact that 32°F suspends the conductivity of nerves is of the utmost importance to surgery, furnishing a convenient means of blocking nerve impulse in a nerve trunk for a desired length of time.

Anesthetics and narcotics, such as ether, chloroform, cocain, chloral, phenol, and alcohol act in the same way. They may be applied locally to a nerve, and if the application be made with care, the irritability and conductivity may be lessened or suspended entirely at this point, and be restored when the narcotic is removed.

Dentists suspend the sensation in the nerve of a tooth by the use of cocain.

It is interesting to note, also that the conductivity of a nerve may be suspended

by the deprivation of oxygen, as is illustrated in cases of suffocation or asphyxiation. This fact illustrates the importance of correct breathing habits, that sufficient oxygen may enter the lungs and the blood, and thus stimulate the conductivity of the nerves, so that they may properly and strongly direct the reflex acts of the body in digestion, assimilation, peristalsis, etc. There is a better, a more natural nerve tonic in the oxygen of the air than in all the drugs of the stores, and if physicians would teach full, deep breathing and teach a patient to stand correctly, so that the lungs, heart and vital organs have room for movement, more permanent results in strengthening depleted nerve force would be gained.

The conductivity of a nerve may also be suspended by pressure, without permanently injuring the fibres, provided the pressure be not too great. This is illustrated by the foot "going to sleep," when the legs are crossed in such a manner as to press upon the nerves controlling the foot.

The conductivity is often retarded by incorrect poise, which displaces some of the vertebra and causes a pressure upon spinal nerves. An upright poise of the spine is essential to free nerve impulse

Reflex
Action.

Some nerve impulses are received and acted upon in the spinal cord, the impulse not reaching the brain; it is therefore, not a conscious act. The action in a muscle, directed by the nerve center, without consciousness, is known as reflex action, because the impulse received by the afferent nerve to the contracting muscle, at the periphery, is reflected from the nerve center. For example, suppose one has just touched, with his hand, a dish that is very hot,-instantly the sensation of heat is flashed over the nerve to the cell in the posterior horn of the spinal cord; the sensory cell hurries a message over to a motor center or cell in the anterior horn of the cord, and a motor impulse flies down the motor fibre causing the hand to be withdrawn before your brain has fairly realized you are burned.

This circle of nerve impulses is called a

reflex act, but because it was a painful experience it rose to the dignity of a conscious act. The same cell, which sent word to the motor cell to have its nerve fibre at once withdraw your hand from the stimulus, also sent a message up to a sensory area in the brain, which registered the pain.

A large part of the reflex activities of the body are done unconsciously, however. If it were not so, the brain would be so fully occupied with the wants and activities of the body that it would have no time for mental exercise in the way of study, business, or bodily education or control. The nerve centers act as the brain's assistants, and, like the assistant in any line of business they execute the work planned; the manager, after instructing an assistant how and what to do leaves the execution to him, thus freeing his own mind from regular details, while he still keeps a general supervision and is notified if anything goes wrong. This is the attitude of the

brain toward the nerve centers, or reflex

arcs.

The manner in which digestion is normally carried on is a good example of unconscious reflex activity. The act of swallowing is a reflex, the presence of food causing a motor impulse to be sent forth to move the muscles of deglutition; the food enters the stomach and its presence stimulates the ends of the sensory nerve in the mucous lining; sensory impulse is received in the spinal cord and an impulse goes back over the secretory nerve, which starts the juices flowing.

Still other sensory impulses are received and motor impulses go back to set up the muscular action called peristalsis.

The presence of water in the stomach or intestines gives the same sensory impulse and peristalsis results, moving the food along the digestive tract. Thus, where digestion is weak, water taken just before a meal starts peristalsis, and the flow of digestive juices. It is in conformity with this principle, that malts or liquors are taken before meals. They