the foot, commonly expressed as "the foot asleep."

The tingling sensations in the hands, arms or legs at night are caused by pressure upon a nerve somewhere along its course; this pressure is usually due to the position of the body during sleep or to defective circulation and a consequent failure to eliminate the carbonic acid gas which presses upon the nerves, and stunts their sensibilities.

As long as the nerves remain in a natural and healthy condition, any portion of the body can incite the muscles to action. Each sensory nerve is supposedly endowed with the property of sensibility to pain, and of conscious sensation, as is illustrated by the nerve of a tooth which may be cauterized so that the nerve is incapable of conveying sensations of pain, yet it may convey the ordinary sensations; the patient may be entirely conscious of just what is going on in the extracting of a tooth and yet be conscious of no pain from it. This is also demonstrated in slight surgical operations;-narcotics so deaden the

sensation of nerves that one is unconscious of pain, but is conscious of movement and all other sensations.

Further experiments with the nervous system may enable us to differentiate between many other forms of sensation.

Investigation has determined that power of motion may be paralyzed though that of sensation remains.

THE BRAIN

The brain is that part of the nervous system which lies within the skull.

The

large convoluted masses of nerve substance are called the cerebrum and the cerebellum. Each mass is divided into halves called hemispheres.

CEREBRUM

FIG. 13. Showing the medulla oblongata and the arrangement of the cerebrum and the cerebellum.

Besides these there are various ganglia of lesser size, situated on or near the under

surface of the brain. These ganglia are as little understood as is the action of the heart or of the sympathetic nervous sys

FIG. 14. Showing the under part of the brain;-the cere brum, the large convoluted mass; the cerebellum, the lower part with striated convolutions; the pons, the white eminence at the base of the brain and at the top of the medulla oblongata; the medulla oblongata showing the base severed from the cord; the optic tract showing the crossing of the nerves; and the olfactory bulb projecting to the frontal lobe of the brain.

The optic nerves have their origin in these nerve ganglia and vision is retained,

even after the cerebrum is removed, providing the nerve ganglia which control vision, lying in the under part of the brain, be left intact.

In some one or all of these small ganglia, resides the power of sensation and motion; this is demonstrated by the fact that unless destroyed by loss of blood, life will continue and the body be still capable of sensation and voluntary movement after the cerebrum and cerebellum have been removed.

The brain, in adult life, weighs about 212 per cent of the body weight; at birth it is 1/3 its mature size and is 12 per cent of the body weight.

The brain grows rapidly, becoming full size by the end of the eighth year, while the body may continue to grow until the eighteenth to the twentieth year.

As the brain develops, the nerves also develop.

The brain is composed of masses of nerve cells and connecting fibres. Each cell is more or less inter-dependent, while having each its own function.