424 



PHYSIOLOGY OF STRESS 



Capacity to carry on efficiently at high 

 temperatures depends on more than general 

 physical fitness. The capacity is highly 

 specific and is acquired. It is a function of 

 repeated exposures and of time (1, 5). The 

 importance of training in anticipation of 

 exposure to excessive temperature can hardly 

 be over-estimated. The critical importance 

 of abundance of drinking water and ade- 

 quate replacement of salt has been experi- 

 mentally demonstrated by Bean and Eichna 

 (5). One is impressed by the rapid and 

 dramatic effects of salt and water deficiency 

 upon psychophysiological status. (See Sec- 

 tion V, 2.) 



The limiting conditions of habitability as 

 shown by Eichna et at. (36) for various com- 

 bat vehicles are dependent on wet bulb tem- 

 peratures. They report that as the upper 

 limit is approached a narrow range of wet 

 bulb temperature differentiates the environ- 

 ment "where work is easy" from "where it is 

 impossible." Theoretically the problem 

 should be to obtain that combination of 

 physiological activities which will make the 

 best use of narrowing possibilities for heat 

 dissipation into the environment. This may 

 involve a complex balancing of conflicting 

 physiological tendencies. Of course, prac- 

 ticable devices for reducing environmental 

 temperature and humidity reduce by that 

 much the demands on the physiological 

 mechanisms. (See Section V, 3.) 



3. Motion Sickness 



It is not possible here to review the ex- 

 tensive research toward a means for control 

 of seasickness (see chapters 18 and 19, on Mo- 

 tion Sickness). However, it is mentioned 

 here as an example of what may be done by 

 well directed investigation of a psychophysi- 

 ological problem. In this case the control of 

 autonomic functions, chiefly by the use of 

 anticholinergic drugs, has provided an im- 

 proved control of one psychophysiological 

 condition. (See section V, 4.) 



4. Odors 



The intensity of the olfactory stimulation 

 and the magnitude of the gastrointestinal 

 responses to it are testified to by repeated 

 reports from the submarines which have 

 undergone prolonged subsurface duty. The 

 intensity of the stimulation becomes obvious 

 only when hfe below is interrupted by watch 

 on deck. This offers convincing testimony 

 to the effectiveness of olfactory fatigue and 

 adaptation as protective mechanisms and 

 contributory factors in habitability. 



B. Stress of Duty 



The physiological concomitants of ac- 

 tivity, in performance of duty, span the 

 gamut of human activity. They may range 

 from those of inactivity and rest through the 

 various degress of activity, mild, moderate, 

 strong, severe, and exhausting. Attending 

 psychological states may range from (a) som- 

 nolence, indifference or boredom through (b) 

 alertness, interest and attention, (c) tension 

 and anxiety, (d) intense effort, to (e) weari- 

 ness, frustration and confusion. Although 

 only the more severe degrees of these condi- 

 tions are commonly identified with stress, 

 we may not ignore the possibility of severe 

 secondary psychological effects correlated 

 with enforced unwelcome inactivity. The 

 adverse effect of monotonous patrolling with 

 no hits has been too frequently noted. (See 

 Section V, 5.) 



The evaluation and measurement of condi- 

 tions of stress may seem to approach an 

 impasse, as have studies of "work" and 

 "fatigue," because of differences in definition 

 and confusion as to the nature of what is 

 measured (3, 6, 8, 10, 31). There may be 

 confusion between decrement in quantity 

 and decrement in quality of output. At one 

 time we may be concerned with (a) physio- 

 logical or organic effects, at another with 

 (b) psychological or subjective effects, and at 

 another with (c) behavioral effects and alter- 

 ations of output and performance. These 

 may be measured respectively (a) by physio- 



