omitant with bodily rest and warmth, and we have no more
right to assign the causation of sleep to cerebral anaemia than to any
other alteration in the functions of the body, such as occur during
sleep.

We may well here summarize these other changes in function:

(1) The respiratory movement becomes shallow and thoracic in type.

(2) The volume of the air inspired per minute is lessened by one-half
to two-thirds.

(3) The output of carbonic acid is diminished by the same amount.

(4) The bodily temperature falls.

(5) The acidity of the cortex of the brain disappears.

(6) Reflex action persists; the knee jerk is diminished, pointing to
relaxation in tone of the muscles; consciousness is suspended.

Analyzing more closely the conditions of the central nervous system,
it becomes evident that, in sleep, consciousness alone is in abeyance.
The nerves and the special senses continue to transmit impulses and to
produce reflex movements. If a blanket, sufficiently heavy to impede
respiration, be placed upon the face of a sleeping person, we know
that it will be immediately pushed away. More than this, complicated
movements can be carried out; the postilion can sleep on horseback;
the punkah-wallah may work his punkah and at the same time enjoy a
slumber; a weary mother may sleep, and yet automatically rock her
infant's cradle. Turning to the histories of sleep walkers, we find it
recorded that, during sleep, they perform such feats as climbing
slanting roofs or walking across dangerous narrow ledges and bridges.
The writer knew of the case of a lad who, when locked in his room at
night to prevent his wandering in his sleep, climbed a partition eight
to ten feet in height which separated his sleeping compartment from
the next, and this without waking.

The brain can carry out not only such complicated acts as these, but
it has been found to maintain during sleep its normal inhibitory
control over the lower reflex centers in the spinal cord.

Thus, in sleeping dogs, after the spinal cord has been divided in the
dorsal region, reflexes can be more easily evoked from the lumbar than
from the cervical cord, because the former is freed from the
inhibitory control of the brain.

The strength of stimulus necessary to pass the threshold of
consciousness and to produce an awakening has been measured in various
ways. It has been determined that it takes a louder and louder sound
or a stronger and stronger electric shock to