552 APPROACH OF SLEEP. 



and the more so since it presents, in the various phenomena of dreams, 

 significant illustrations of the manner of action of the nervous system. 



All animals sleep. Many, perhaps most,- dream. The necessity for a 

 season of repose arises from the preponderance of the waste of the sys- 

 tem ove/ its repair during our waking hours. By bringing the animal 

 functions into a condition of rest, an opportunity is afforded for renova- 

 tion, and the equilibrium can be maintained. 



In early infancy, when it is necessary for the nutritive operations to be 

 . ., carried forward with the utmost vigor, and attended with as 



Causes of the &. 



necessity for little waste as possible, the whole time is spent in sleeping 

 and eating. The waking period is gradually increased as the 

 child advances, but not so as to make it continuous, for the day is broken 

 into intervals of sleep. Even at three or four years of age we sleep more 

 Duration and tnan once a ^ a j- ^ n mature life eight hours are on an aver- 

 depth of sleep. a g e required, but the precise time varies with different indi- 

 viduals, and even with the same individual in different constitutional 

 states. The time is not, however, always a true measure of the amount 

 of rest, for sleep varies very much in the degree of its completeness or 

 intensity ; there is a slumber so disturbed that we are unrefreshed by it, 

 and a sleep so profound that we awake weary. Old age, as it advances, 

 admonishes us to spare the system as much as we may, for repair is con- 

 ducted with difficulty ; and this period, characterized by its resemblance 

 in so many respects to childhood, like it, is often marked by frequently- 

 recurring and prolonged slumber. Moreover, various accidental and 

 other circumstances are liable at all times to disturb its proper periodic- 

 ity a warm afternoon, a hearty dinner, an ill-ventilated apartment, mo- 

 notonous sounds, the attention devoted to one object, bodily quiescence, 

 ceasing to think, the use of narcotics, extreme cold, a horizontal posi- 

 tion, &c. 



Sleep is commonly preceded by a sense of drowsiness of more or less 

 Approach of intensity, which is gradually followed by a loss of sensibility, 

 sleep. Objects cease to make an impression on the eyes, the lids be- 



come heavy and close. If we are not in the horizontal position, but re- 

 quire muscular support, as in sitting, the head droops, and the hands seek 

 a support. Successively the senses of smelling, hearing, and touch pass 

 away, as the sight has done ; but, before this progress is completed, we 

 start at any sound or disturbance, voluntary muscular action being in- 

 stantly assumed, though in the midst of a surprise. "We are nodding. If 

 we are in the horizontal position, as in bed, the body is thrown into a 

 form requiring the least muscular exertion the limbs are semiflexed. 

 As sight, smell, hearing, touch, again in succession fail, all voluntary mo- 

 tions cease, those which are now executed being of a purely automatic 

 kind. The eyes are turned upward and inward, the iris is contracted, 



