THE HYGIENE OF THE NERVOUS SYSTEM 173 



measuring the intensity of stimuli, such as sounds or 

 electric shocks required to wake the sleeper. After 

 the first hour a shoaling of sleep soon begins and goes 

 on at such a rate that one would predict waking within 

 two or three hours. Instead of this there is a long 

 period of light sleep from which one is easily roused. 

 This is not the same as saying that one is easily kept 

 awake, for the shallow sleep toward morning is readily 

 resumed after an interruption. The nervous, shock 

 experienced when one is awakened from the deep sleep 

 of midnight is vastly more severe than the excitement 

 created by the alarm clock at 6 a.m. 



Certain writers on hygiene, having in mind the 

 maximum efficiency of the man, urge that . sleep be 

 reduced to six or to five hours a day. It is hard to de- 

 cide whether such teaching is universally to be applied. 

 There would seem to be a real danger of overtaxing 

 the nervous system. Yet it is probably true that many 

 people waste time in sleep. This is most apt to be the 

 case with heavy eaters who are commonly heavy sleepers 

 as well. Overeating seems to produce changes in the 

 composition and distribution of the blood that favor 

 drowsiness. Consistently with this light eaters are 

 often sufferers from insomnia.- 



When we wake from sleep we may or may not recall 

 that we have been dreaming. If we have recollections 

 of the mental currents that have run their course while 

 we slept we can usually say whether we have been much 

 concerned with the cares and interests of our present 

 life or whether we have been watching curious pictures 

 founded on scenes long past and, as we supposed, for- 

 gotten. The best sleep is probably that which seems 

 to have been dreamless as we look back upon it but if 

 there are dreams it is not desirable that they should be 

 of actual, present affairs. It is a sign of nerve-fag when 

 the thoughts of the night closely resemble those of the 

 day. When a healthy man goes to sleep he may have very 

 much the same experience as though he entered a moving 



