pulse is conveyed along the nerves, the electrical current is diminished in force. This would indicate that a sensory stimulation, being conveyed along the nerves for any great length of time,-such as is the case in derangement of any organ or tissue of the body,-the electrical current to the affected part being diminished, the nourishment to the nerve would be restricted.

All experiments have failed to determine just what this force flowing through the nerve is; later scientists have decided however, to term it "nerve principle" or "nerve impulse' until a more satisfactory solution of its nature has been reached.

Perhaps most physiologists believe the nerve impulse to be a progressive wave of chemical change, which is started at one end by the stimulus and is then self-propagated along the fibre, by change in the position of the molecules in the axon.

It has not been shown that waste is liberated in this chemical wave, however, as is the case of chemical action in muscles.

It has been found by the test of the galvanometer that there is an electrical current, independent of the nerve impulse, continuously passing through every nerve in a state of rest, this electrical current is more or less affected by the electricity in the air. Perhaps enough is known to justify the general view, that the electrical energy displayed, is derived, in the long run, from the metabolism of the cells;-a metabolism, which consists in the splitting of the substances, (whatever they may be) in the protoplasm of the cells.

It is definitely known that oxygen is consumed in this force, and the necessity of fresh air, during both waking and sleeping hours, is imperative.

Nerve impulse is increased, as are all metabolic changes, by friction produced by exercise, but more especially by friction produced by the chemical action of oxygen. Oxygen is thus an important element in nerve tonicity. For nerve strength, too great emphasis cannot be laid upon the importance of habits of full breathing..

Origin of

Nerve
Force.

The fact that the nerve force is originated in the gray matter is illustrated by cutting a nerve in two. All sensation and motion ceases in the portion supplied by the nerve which has been severed, until such time as the wound may heal and the severed part be knitted together;-then the power of sensation returns.

No nerve conveys impulse, either inward or outward, unless it be connected with gray matter in the nerve cells. This still further goes to prove the neuron theory that the axis cylinders are processes of nerve cells.

Waller showed that, if a nerve be severed, the peripheral end containing the axis cylinder will degenerate in a few days, while the central stump, which is connected with the nerve cell, remains intact, except for a short distance from the region contiguous to the point of severance. This experiment demonstrates that the nerve fibres derive their nutrition and receive their motor impulse from the nerve cells, and that there can be no sensation nor mo

tion beyond the point of severance;-the severed part of the body is as free from connection with the brain, and thus from consciousness, as if it were a foreign body. The necessity of freedom and strength of nerve centers is therefore readily understood.

If the chemical constituents of the gray matter in the nerve centers were known it would be an easier matter to build up the strength of the nerve centers, by the right foods. The only chemical constituent known to be necessary is oxygen.

Rapidity of Nerve Current.

In the cerebro spinal system of nerves, the nerve impulse is rapid, but not as rapid as waves of light or of electricity. It flows about 110 feet per second, but its exact velocity has not been determined. Supposing it to travel 110 feet per second, an impulse to go from the foot to the brain would require about one-twentieth of a second and the same to return.

Impulse, however, is conveyed through the sympathetic nerves much more slowly. This is illustrated by a person entering a

dark room from the bright sunlight. The pupil of the eye, in the sunshine, has been so contracted as not to admit an undue amount of light, and in going into the darkened room, in order to admit more light, the pupil must greatly enlarge. This impulse to enlargement is conveyed through the sympathetic nerves and it Takes an appreciable time for the pupil to readjust itself. This adjustment of the pupil is entirely beyond our conscious control, as are all acts of the sympathetic nervous system, except as we control our thoughts and emotions.

The cerebro spinal nerves are the only nerves of the body directly within the control of the will.

Variations in temperature influence the irritability of the nerves and the rate at which an impulse is carried, the velocity increasing with a rise in temperature. Where the nerve force is dormant, cold baths are most efficient in arousing it.

Generally speaking, the limit of conductivity, lies between 32°F and 82°F. Cooling a nerve to 32°F, or the freezing point