in rehdon (o Dise(^8$. 43 



ing of want of proper balance to the frame-^all indicating some 

 cause present which tends more or less to disturb the equality 

 of circulation through this organ. 



In fact, the ordinary phrases of heaviness and lightness of 

 air (however misplaced or even inverted their use) prove the 

 general consciousness of these changes in their slighter influ- 

 ence on the body. It may be difficult to say through what 

 organ or function this feeling is chiefly conveyed ; but probably 

 it is a compound effect of the changes in circulation, in which 

 the sensorium, the lungs, and the muscular system, all partici- 

 pate. Even the organs of digestion seem to be affected, di- 

 rectly or indirectly, by the same causes. Without referring 

 to the doubtful instance of vomiting produced in highly rare- 

 fied air, 1 think I have observed frequent disturbance both in 

 the sensations and functions of the alimentary canal, under any 

 rapidly diminished weight of the atmosphere, or where its 

 changes were more frequent than usual. I have remarked in 

 the preceding chapter on the indications of disturbance to sleep 

 from the same cause. 



All these inferences, however, are rendered uncertain by the 

 great difficulty of simplifying the conditions which belong to 

 them, where the physical causes concerned are so unceasingly 

 blended in their operation. It may be, for instance, that what 

 is attributed to changes of weight of air, really belongs to elec- 

 trical changes in the atmosphere, producing or attending the 

 former. Another more familiar case of ambiguity, is that of the 

 sensations experienced in reaching a high mountain- summit. 

 Though often attributed to rarefaction of the air breathed, 

 I doubt not (on my own observation as well as that of others), 

 that they are chiefly owing to the expenditure of bodily power 

 that has been incurred by muscular action, hurried breathing, 

 and quickened action of the heart. These sensations in great 

 part subside, when the immediate causes of lassitude and dis- 

 order are removed. Or, if we yet need explanation of that 

 singular sense of fatigue in the limbs, which is alleged to occur 

 when walking in elevated regions, even without the toil of as- 

 cent, we may perhaps find it in a suggestion of Humboldt ; 

 whose sagacity is ever awake to all natural phenomena, even 

 such as pass unheeded by others from their seeming familiarity. 



