140 PHYSIOLOGY FOR NURSES 



there is an appreciable fall in body temperature, the 

 lowest occuring between midnight and three in the 

 morning. 



Not all of our senses fall asleep at the same time or 

 to the same degree. Light is first lost, in fact we de- 

 liberately cut off the light by closing the lids. Hearing 

 is never so completely abolished and sensitiveness to 

 touch is present in all but the most profound slumber. 

 Taste and the sense of smell are almost completely 

 abolished. It seems that loss of sensibility of all kinds 

 is due to a change in the cortex of the brain and not in 

 either the peripheral nerve terminals or in the conduct- 

 ing paths. While our muscles are relaxed, they will 

 carry out coordinated movements without our being 

 conscious either of the stimulus, like tickling the nose or 

 lids, or of the movement to brush away the offending 

 body. Of course, frequent repetition of the stimulus 

 will awaken one. Sleep, however, while mainly affect- 

 ing the brain, is not confined to it. All of our tissues 

 and organs sleep. 



There are many theories of sleep but the chief ones 

 are chemical or circulatory. 



A chemical theory supposes that the body forms, dur- 

 ing waking hours, substances of a more or less poison- 

 ous character which, when accumulated in sufficient 

 quantity prevent (inhibit) the activity of the cortex; 

 or that an increase in the acid waste products of the 

 body will exercise the same influence. 



A circulatory theory explains the periodic occur- 

 rence of sleep by assuming that there is an absence of 

 sufficient blood in the brain (anemia) to keep up its 

 normal activity, and that sleep follows, basing the 

 theory largely on the well-established fact that experi- 

 mental interference with the blood supply of the brain 



