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Proceedings oj the British Association. 



amount of carbon in the daily food of an adult man, taking mode- 

 rate exercise, is 14 oz., which require 37 oz. of oxygen for their conver- 

 sion into carbonic acid. But it is obvious, as the inspired oxygen can 

 be removed only by its conversion into carbonic acid and water, 

 that the amount of food necessary for the support of the animal body, 

 must be in direct ratio to the quantity of oxygen taken into the system. 

 Thus a child, in whom the organs of respiration are naturally in a state 

 of great activity, requires food more frequently, and in greater propor- 

 tions to its bulk, than an adult, and is also less patient of hunger. A 

 bird, deprived of food, dies on the third day ; whilst a serpent, which 

 inspires a mere trace of oxygen, can live without food for three months. 

 The capacity of the chest in an animal, is a constant quantity. We there- 

 fore, inspire the same volume of air, whether at the pole or the equator. 

 But the weight of the air, and consequently of the oxygen, varies with 

 the temperature. Thus an adult man takes into the system daily 

 46,000 cubic inches of oxygen, which if the temperature be 77°, weigh 

 32J oz. ; but, when the temperature sinks down to the freezing point 

 (32°), it will weigh 35 oz. Thus an adult in our climate in winter 

 may inhale 35 oz. of oxygen ; in Sicily he would inspire only 28| oz. ; 

 and, if in Sweden, 36 oz. Hence we inspire more carbon in cold wea- 

 ther, 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 our own climate, the difference between summer and winter in the car- 

 bon expired, and therefore necessary for food, is as much as an eighth. 

 Even when we consume equal weights of food, an infinitely wise Crea- 

 tor has so adjusted it as to meet the exigencies of climate. Thus the fruit 

 on which the inhabitants of the south delight to feed, contains only 

 12 per cent, of carbon, whilst the bacon and train oil enjoyed by 

 the inhabitants of the Arctic regions, contain from 66 to 80 per cent, of 

 the same element. Now the mutual action between the elements of 

 food and the oxygen of the air, is the source of animal heat. All living 

 creatures, whose existence depends on the absorption of oxygen, pos- 

 sess within themselves a source of heat, independent of the medium in 

 which they exist. This heat, in Professor Liebig's opinion, is wholly 

 due to the combustion of the carbon and hydrogen contained in the 

 food which they consume. Animal heat exists only in those parts of 

 the body through which arterial blood (and with it oxygen in solution) 

 circulates. The carbon and hydrogen of food, in being converted by 

 oxygen into carbonic acid and water, must give out as much heat as if 

 they were burned in the open air. The only difference is, that this 

 heat is spread over unequal spaces of time ; but the actual amount 



