A smaller quantity of carbonic acid is eliminated in sleep, the decrease being about sixteen per cent. But that condition is not due to sleep. It is due to many other factors such as the absence of light, etc. The nature of the food taken before retiring has also a notable influence on the quantity of carbonic acid eliminated by the sleeper; the quantity varies from seventy five per cent after a meat supper to ninety per cent after a diet of starches. The sweat glands of the skin secrete more actively in sleep than in waking life, which is also a vagotonic symptom and is also due to the fact that the sweat centre is easily affected by carbonic acid. This increase in the activity of the skin accounts for the decrease we notice in the activity of the kidneys. (More urine is produced on cold days when the perspiration is scanty than on hot summer days.) The lowering of the temperature in sleep is simply a result of inactivity, not of sleep. We know that many pains, especially neuralgias, disappear in sleep. Many of those ailments, however, are of a neurotic origin and constitute a form of escape from reality. When reality has been practically abolished by unconsciousness, they are no longer "needed." Experiments made on instructors of the University of Iowa who were kept awake for ninety hours showed that the weight of the subjects increased during the experiments, decreasing later when the subjects were allowed to resume their natural life and to sleep. The increase was solely due to the fact that during the experiments, the subjects were relieved of their duties, remained idle in the psychological laboratory and hence consumed less organic matter than if they had led an active life, preparing their courses and teaching several hours a day. It has been stated many times that a form of motor paralysis sets in during sleep. Yet we all know of the many motions performed by every sleeper, turning from side to side, drawing or pushing away the bed clothes, removing stimuli applied to the face, talking, not to mention, of course, sleep walking. Sleep does not even mean complete muscular relaxation, for sentinels have been observed who could sleep standing; some people sleep sitting up in their chairs. Many animals, birds, bats, horses, sleep in positions which make muscular relaxation impossible; when their balance is disturbed by an observer, they re-establish it without awaking. Sleeping ducks keep on paddling in circles to avoid drifting against dangerous shores, etc. In other words, there is not a part of our body which ceases in sleep to perform its specific work. Our lungs continue to breathe, our heart to send blood to all parts of the body, our glands secrete various chemicals; we hear, smell and to a certain extent, see. The lowering of our eyelids is simply a half-conscious effort to remove sight stimuli. Our nails and hair continue to grow, although, for that matter, they do so for some time even after death.