408 



MOTION SICKNESS, II 



produced by rotating guinea pigs when the 

 otoHthic apparatus has been paralyzed by 

 centrifugation. Previously, T. G. Brown 

 (cited in 21) had shown that the respira- 

 tory changes evoked by up and down move- 

 ments were still present after removing both 

 otohths. 



Studies Correlating Incidence of 

 Motion Sickness with Physical Char- 

 acteristics OF the Imposed Motion 



Studies falling under the heiading of this 

 section have apparently never been made at 

 sea; therefore, we shall be concerned here 

 only with laboratory experimental work. 

 In view of the absence of data on the motion 

 of vessels (see above), it is not surprising to 

 find that the devices to induce sickness con- 

 structed during the war developed motions 

 resembling ship or aircraft motion only in 

 a general way. It seems also to be true 

 that in the majority of cases such devices 

 (e.g., hand-pushed swings) moved in a very 

 complicated and not always reproducible 

 fashion. One must therefore keep in mind 

 the uncertainty surrounding the physical 

 implications of the results. 



Among the more definitive findings of war- 

 time research are those having to do with 

 the relation between head position and in- 

 cidence of sickness on the swing. Manning 

 and Stewart (17), using large numbers 

 (70-100) of subjects per position, demon- 

 strated the considerable superiority of the 

 supine position in avoiding sickness on the 

 swing. In their experiments the sitting 

 position and the prone position both were 

 associated with a comparatively high inci- 

 dence. This was also the essential result of 

 Mclntyre (19). In a related study, Howlett 

 and Brett (13) concur w^th the general 

 finding that when the meatal-canthal line is 

 parallel to the radius of the swing the inci- 

 dence is least, and that when it is normal the 

 incidence is greatest (however, these authors 

 draw additional conclusions to those men- 

 tioned presently). Thus, for whatever ac- 

 celerations the swing imposes, there appears 



to be established a directional effect. It is a 

 difficult and somewhat harder problem to 

 discover the time course of the accelerations, 

 and a harder problem still to decide which 

 receptors are involved. If a subject is 

 swung with his head in some constant rela- 

 tion to the swing structure, as when held by 

 a head rest (6), then the most natural way to 

 resolve the accelerations is into radial and 

 tangential components. An interesting at- 

 tempt to do this has been made by Cipriani 

 (7), on the assumption that the swing is an 

 isolated conservative system." He finds 

 that the experimental conditions used with 

 the Canadian swing are a period of 2 sec. 

 and a radial acceleration maximum of about 

 0.7 g. The maximum tangential accelera- 

 tion exclusive of the unknown contribution 

 by the push is of the order^^ of 0.64 g. 

 Cipriani regards the larger tangential ac- 

 celeration as ineffective "since it affects 

 equally the skull and its mobile contents." 

 With this conclusion the present author dis- 

 agrees, since the inertial terms of equation 

 (3) depend precisely on the tangential ac- 

 celeration. The possible effect of angular 

 acceleration in their experiments was seem- 

 ingly overlooked by the Canadian authors. 

 Apparently on the assumption that only a 

 radial acceleration operates effectively in the 

 swing, Howlett and Brett have taken the 

 aforementioned relation between the meatal- 

 canthal line and incidence to suggest that 

 the utricles are the receptors involved, since 

 the plane of their maculae includes the line. 

 (It is of course also true that the fixing of j 

 this line fixes other structures, for example,' 

 the vertical canals, in the correspondingly 

 susceptible position.) These authors find 

 further that under their hypothesis the_ 

 utricular macula would have to be stimu- 

 lated more when the otolith is pressed into' 



" Actually, of course, it is neither isolated (be- 

 cause energy is constantly imparted to it by ex- 

 ternal pushing) nor conservative (because thftrft| 

 is friction). 



'2 This is a rather uncertain calculation becausel 

 it involves formulae which assume that the oscil- 

 lations are small, and these are not. 



