16 EFFECT OF HEAT ON THE OXYGEN CONSUMED. 



by vapor in warm air is filled by air itself in winter ; it 

 contains, for the same volume, more oxygen in winter 

 than in summer. In summer and in winter, at the pole 

 and at the equator, we respire an equal volume of air ; 

 the cold air warmed during respiration in the air passages 

 and pulmonary cells, acquires the temperature of the 

 body. To introduce into the lungs a given volume of 

 oxygen, less expenditure of force is necessary in winter ; 

 and for the same force, more oxygen is inspired. 



In an equal number of respirations we consume more 

 oxygen at the level of the sea than on a mountain. The 

 quantity both of oxygen inspired and of carbonic acid ex- 

 pired, must therefore vary with the height of the barometer. 



The oxygen taken into the system is given out again 

 in the same forms, whether in summer or in winter ; 

 hence we expire more carbon in cold weather, and when 

 the -barometer is high, than we do in warm weather ; 

 and we must consume more or less carbon in our food 

 in the same proportion ; in Sweden more tnan in Sicily ; 

 and in our more temperate climate a full eighth more in 

 winter than in summer. 



Even when we consume equal weights of food in 

 cold and warm countries, infinite wisdom has so ar- 

 ranged, that the articles of food in different climates 

 are most unequal in the proportion of carbon they con- 

 tain. The fruits on which the natives of the south 

 prefer to feed do not in the fresh state contain more 

 than 12 per cent, of carbon, while the bacon and train 

 oil used by the inhabitants of the arctic regions contain 

 from 66 to 80 per cent, of carbon. 



It is no difficult matter, in warm climates, to study 



