330 



SLEEP-WAKEFULNESa CYCLE 



of days or weeks, and it may be completely 

 abolished by disease, when a person is un- 

 conscious for a long time (as in encephahtis). 

 The fixity or repetitiveness of the diurnal 

 body temperature curve has a significance 

 far beyond serving as an index of one's 

 adjustment to the 24-hour astronomical 

 cycle of the earth. Efficiency of perform- 

 ance and the degree of alertness during the 

 customary waking phase of the cycle seen 

 to conform to the rise and fall of the body 

 temperature. Thus, immediately upon 

 awakening in the morning, when one's body 

 temperature is about the same as (or slightly 

 lower or higher than) at the time of going 

 to bed the night before, performance, under 

 laboratory conditions, of any of several men- 

 tal or physical tasks chosen for testing pur- 

 poses was found to be as poor as (or slightly 

 better or worse than) at the time of going 

 to bed, whether the criterion of performance 

 was speed or accuracy. During the morn- 

 ing, and sometimes early afternoon, as long 

 as the body temperature is on the up-grade, 

 efficiency of performance increases, reaching 

 either a definite peak or an extensive plateau, 

 very much as does the body temperature 

 curve. Later in the day, sometimes not till 

 the evening, the body temperature curve 

 turns downward, and, with this change 

 in direction, there begins a progressive de- 

 chne in efficiency of performance. The low 

 at bedtime, as already indicated, is about 

 the same as immediately upon getting up, 

 representing a characteristic "drowsiness 

 level." If one remains awake during the 

 entire night, both temperature and perform- 

 ance fall below their drowsiness levels, reach- 

 ing their minima between 2 and 4 a.m., 

 when it is hardest to keep awake. Then 

 there begins an upswing which crosses the 

 drowsiness level at the usual getting-up time. 



Ship Operation and the 



Sleep- Wakefulness 



Cycle 



Since operation of a ship under way re- 

 quires a round-the-clock schedule of activ- 



ities, the crew works [under a timing of 

 watches usually involving a "4 hours on and 

 8 hours off" routine. With such a schedule, 

 one or another watch section is at a dis- 

 advantage with respect to meals and recre- 

 ation, as well as sleep, since on most surface 

 warships the members of the crew are not 

 allowed to sleep in the daytime. In addi- 

 tion, during general quarters (one hour in 

 the morning and one in the evening) all 

 hands must be at their battle stations. This 

 requires two hours more per day of the 

 other two watch sections than of the 4-8 

 and 16-20 section which is on watch at that 

 time anj^way. To be fair to all, watches 

 are often rotated by the system of "dogging" 

 the watch: the 16 to 20 o'clock watch is 

 split in two, with the new section going on 

 watch at 18 o'clock. From the standpoint 

 of establishing and maintaining a regular 

 diurnal cycle of sleep and wakefulness, the 

 system of dogging the watch at frequent 

 intervals is disastrous. Practically all men 

 retain the shore-type body temperature and 

 efficiency curves, which makes them sleepy 

 during night watches. Thus, during these 

 hours of darkness, when sudden attacks are 

 likely to occur and when special alertness 

 is required, the majority of the crew is fast 

 asleep, and the few who are awake are at 

 their least efficiency. 



For the purpose of insuring that a por- 

 tion of the crew is wide-awake and ready for 

 action at any hour of the day and night, the 

 routine that prevails on submarines has sev- 

 eral advantages over that of surface ships. 

 There is no reveille and usually no daily 

 general quarters requiring the entire crew 

 to turn out. The men are permitted to 

 sleep during daytime hours, and since prac- 

 tically all work is done under artificial light, 

 the difference between day and night is min- 

 imized, or absent. If the commanding offi- 

 cer so desires, the watch may remain fixed 

 for the entire duration of a cruise, or may 

 be rotated at only infrequent intervals. The 

 evening meal hour may be moved from 17 : 30 

 to 19:30, thus making it unnecessary to 



