738 A TEXTBOOK OF PHYSIOLOGY 



by suggestion, generally, but not necessarily, verbal in nature. It is 

 essential that the subject have the idea of sleep and be prepared to 

 surrender himself to the treatment of the operator. 



Experiment shows that the condition differs in several respects 

 from normal sleep. The bloodvessels of the skin are constricted, 

 the volume of the limbs is diminished, the blood-volume of the face, 

 and probably the circulation through the brain, is increased. The 

 pulse and respirations are usually quickened. The individual becomes 

 an automaton. The judgment powers of the higher centres are in 

 abeyance, but the receptive centres are alert. Thus, the subject may 

 unhesitatingly perform an order if not too extravagant or believe a 

 fact suggested to him. If told to perform a certain act at a certain 

 hour, the act may be done; if told that he is paralyzed, the subject 

 may act as if such were indeed the case. 



Hypnosis has been practised in medicine, but is of doubtful value, 

 except, perhaps, for certain nervous disorders. Operations can be 

 performed in the hypnotic state, but such operations are better per- 

 formed under ordinary narcosis. The whole subject is surrounded 

 by quackery and liss. 



Hibernation. Certain animals retire at times tqjEheir skelters and 

 pass into a torpid state known as " hibernation.".- Such animals 

 include insects, amphibians, reptiles, and mammals such as the dor- 

 mouse, squirrel, hedgehog, marmot, bat, beaver, and bear. As the 

 name implies, hibarnation generally occurs with the approach of 

 cold weather, but this is not necessarily the case. Some animals 

 begin to hibernate in summer, or will hibernate when kept in a 

 warm room away from cold. Cold is not the cause of hibernation; 

 in fact, intense cold stops it. It is a device for securing the continu- 

 ance of life during a period when food is lacking. Before hibernating 

 the animal puts on fat. It has been suggested that the state is a 

 narcosis induced by the accumulation of C0 2 within the body. The 

 body temperature falls, the excitability of the nervous system is 

 depressed, the frequency of respiration is slowed, and the heart 

 force and frequency are much reduced. 



The awakening from hibernation is characterized, in warm-blooded 

 animals, by a sudden rapid rise of body temperature, accompanied 

 by a greatly increased discharge of carbon dioxide from the body. 



