Og-j^, OK 6EASICKNES3. 



different states of the chest. It is probably from this cause, 

 Headach. that, in severe headachs, a degree of temporary relief is ob- 

 tained by occasional complete inspirations. 

 The respira- In seasickness also the act of inspiration will have some 



tjoii should tendency to reUeve, if veyulated so as to counteract any 

 counteract the •' <. , , i • , ■ , , 



pressujeof the temporary pressure ot biood upon the braui ; but the c>ause 



hloodoii the ^f gugi-, pressure requires first to be investigated. 



'■ Ail those who have ever suffered from seasickness (tvith^ 



which is pro- *^"^ being giddy) will agree, that the principal uneasiness is 



duced by the felt during the subsidence of the vessel by the sinking of 



theTe^"d? ° ^^^^ "'^^'*^ *^" which it rests. It is during this subsidence, 



that the blopd has a tendency to press with unusual force 



upon the brain. 



If a person be supposed standing erect upon deck, it is 

 evident that the bruin, which is uppermost, then sustains no 

 pressure from the mere weight of the blood, and that the 

 vessels of the feet and lower parts of the body must con- 

 tract, with a force sufficient to resist the pressure of a 

 column of blood of between five and six feet from the head 

 downwards. 



If the deck were by any means suddenly and entirely 

 removed, tlie blood would be no longer supported by its 

 vessels; but both. Tvo.uld fall togethi^r with the same velocity 

 by the free action of gravity ; and the same contraction of the 

 vessels which before suppor'ed the weight of the blood 

 would now occasion it to press upon the brain, with a force 

 proportional to its former altitude. 



In the same manner, and for the same reason, during a 

 more gradual subsidence of the deck," and partial removal 

 of support, there must be a partial diminution of the pres- 

 sure of the bipod uppq its vessels, and consequently, a 

 ■partial reaction upon the brain, which would be directly 

 counteracted by ja full inspiration. 



The consequence pf external motion upon the blood will 

 be best elucidated by what may be seen to occur iu ^ 

 column of mercury similarly circumstanced. 

 The ikctillus- A barometer, when carried out to sea in a calm, rests at 

 "^^^^ • tbe same height at which it would stand on shore ; but, 



when the ship falls by subsidence of the wave, the mercury 

 }9 seen apparently to ribe in the tube that contains it, be- 

 cause 



