REFERENCES 



393 



other situations in which transient or peri- 

 odic accelerations are encountered. Ani- 

 mals, other than man, share the predisposi- 

 tion to motion sickness, and dogs in 

 particular have been found to be useful for 

 experimental studies of the problem. 



Motion siclvness is primarily the result of 

 stimulation of the vestibular apparatus of 

 the inner ear by acceleration. Destruction 

 of the vestibular apparatus or its afferent 

 nerve fibers results in immunity to motion 

 sickness. Recent research defines motion 

 sicloiess with greater specificity, and non- 

 labyrinthine factors are now considered to 

 be less important. 



Continued motion sickness, e.g., on a long 

 cruise at sea, may require hospitilization of 

 individuals due to protracted vomiting. Al- 

 though the number of cases who are unable 

 to show any adaptation to motion is small, 

 these individuals represent a serious problem 

 in the military services. 



It is improbable that a totally resistant 

 group could ever be successfully screened 

 from the population at large because of the 

 large proportion of individuals who may be 

 made motion sick. Susceptibility to motion 

 sickness may be tentatively regarded as a 

 general factor for all situations involving 

 acceleration. This quality of susceptibility 

 may be utilized to screen personnel in mili- 

 tary or other situations where a more resis- 

 tant population is desired. With available 

 means of detecting susceptibility to motion 

 sickness, e.g., questionnaires and swings, a 

 significant reduction could be made in the 

 number of unadaptable or the very suscep- 

 tible persons being assigned to critical tasks 

 in military service. 



Of all auxiliary factors attending the ap- 

 pearance of motion sicloiess, visual orienta- 

 tion and position of the head with respect 

 to the direction of the applied acceleration 

 appear to be most important. The magni- 

 tude of reduction of motion sickness by con- 

 trol of head position or vision is, in general, 

 larger than the protection afforded by 

 drug therapy. 



Drugs have been found to be effective in 

 the reduction of motion sicloiess, and pro- 

 tection up to 60 percent has been reported. 

 Suggestion accompanying the use of medica- 

 tions is not regarded as significant, since 

 studies have shown that the incidence of 

 motion sickness is about the same in un- 

 treated as in placebo groups, whereas 

 groups receiving active medication have a 

 significantly lower incidence. 



Although there are marked individual dif- 

 ferences in susceptibility to motion sickness, 

 the basis for such differences are not appar- 

 ent. Few measurable traits either physio- 

 logical or psychological have been found to 

 be significantly related to susceptibility. 

 Individual differences in personality traits 

 do not contribute to an important degree to 

 variations in susceptibility. Motion sick- 

 ness is decidedly not a psychogenic afflic- 

 tion, although there are undoubtedly indi- 

 viduals in whom unusual emotional states 

 may facilitate the appearance of symptoms, 

 once the primary conditions of acceleration 

 are met. 



Although present knowledge of motion 

 sickness can be applied to reduce the prob- 

 lem of motion sickness, several aspects need 

 further research. Continued investigation 

 into the basic nature of motion sicloiess 

 with attention to refining the criteria of 

 sickness and improving the rehability of the 

 various measurements should result in still 

 further gains in control of the problem. 



References 



1. Anonymous. Critical study of seasickness 



remedies. Royal Nav. med. Bull., 1943, No. 

 4, 3-6. 



2. Anonymous. Airsickness in military avia- 



tion. Summary Report No. 2, War De- 

 partment, Army Air Forces, No date. 



3. Anonymous. A psychological and physio- 



logical survey of aircrew enlistments in the 

 Royal New Zealand Air Force. NRC, New 

 Zealand File, Fitness for Aircrew, No- 

 vember 1944. 



4. Agin, L. J. Airsickness and related psy- 



chosomatic complaints. Air Surgeon's 

 Bull, August 1945, 2, 235-236. 



