HIBERNATION 225 



as the cause of the anemia of the brain resulting in sleep. In 

 the third set of theories sleep is supposed to be due to a separation 

 of the dendrites of the brain cells due to an active contraction 

 or to an intrusion of neuroglia cells between them. 



During sleep the capability of the nervous system to trans- 

 mit impulses is not entirely lost. The cerebral cortex is most 

 affected, the spinal cord least. The close relation between 

 dreams and external stimuli is well known, and it has been 

 proved experimentally that vasomotor changes, induced by 

 external stimuli, may take place without awakening the sleeper. 



The period of deep sleep is short and falls within the first two 

 hours after its onset. During this time the pulse and breathing 

 are slower, the intestines and bladder are at rest, the output 

 of carbon dioxide is lessened, and the consumption of oxygen 

 still more so; metabolism is less vigorous and the temperature 

 falls. The respiration is said to become thoracic in type, and 

 to take on a more or less pronounced Cheyne-Stokes rhythm. 

 The visual axes are directed upward and inward, but the pupils 

 are contracted. The latter is peculiar, since an absence of light 

 should bring about dilatation. This is connected perhaps with 

 important actions taking place in lower levels of the brain. 



Loss of sleep is more injurious than starvation. Dogs have 

 recovered from a period of starvation of twenty days, but a 

 loss of sleep of five days proved fatal. The body temperature 

 fell 8 C. below normal and the reflexes disappeared. The red 

 blood corpuscles first were diminished, but later increased in 

 number. Postmortem examination revealed widespread fatty 

 degeneration and cerebral hemorrhage. 



In experiments made by Patrick and Gilbert, three subjects 

 were observed for ninety hours while being deprived of sleep. 

 The gain in weight which resulted was lost during the first sleep 

 after the experiment. A decreased pulse rate and a lowered 

 body temperature were observed. In general, there was a loss 

 of all powers except in acuteness of vision, which was increased. 



Hibernation. This is connected closely with sleep, occurring 

 periodically in many groups of animals and in a few mammals. 

 It is characterized by a lessened metabolism resulting from a 

 fall of the external temperature, and may be produced artifi- 

 ficially in summer by cold. The heart beats very slowly and 

 not very vigorously, w r hile respiration is very slow and feeble, 

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