DEPENDENCE OP PLANTS AND ANIMALS. 313 



high, does not require so great an amount of, chemical 

 action to go on within him for the purpose of main- 

 taining the requisite animal heat; consequently his 

 Maker has surrounded him with fruits and grains which 

 constitute his food. 



As we advance to the colder regions of the earth 

 man becomes a flesh-eater, and his carnivorous appe- 

 tite increases as the external temperature diminishes. 

 Eventually we reach the coldest zones, and the human 

 being there devours enormous quantities of fat to 

 supply the necessities of his condition. 



It must necessarily follow, that the inhabitants of the 

 tropics do not produce so much carbonic acid as those 

 who dwell in colder regions. In the first place, their 

 habits of life are different, and they are not under the 

 necessity of maintaining animal heat by the use of arti- 

 ficial combustion, as are the people of colder climes. 

 The vegetation of the regions of the tropics is much 

 more luxuriant than that of the temperate and arctic 

 zones. Hence an additional supply of carbonic acid is 

 required between the torrid zones, and a less quantity 

 is produced by its animals. These cases are all met by 

 the great aerial movements. A current of warmed air, 

 rich in oxygen, moves from the equator towards the 

 poles, whilst the cooler air, charged with the excess of 

 carbonic acid, sets in a constant stream towards the 

 equator. By this means the most perfect equalization 

 of the atmospheric conditions is preserved. 



The carbonic acid poured out from the thousand 

 mouths of our fiery furnaces, produced during the 

 laborious toil of the hard-working artizan, and ex- 

 haled from every populous town of this our island 

 home, is borne away by this our aerial currents to 

 find its place in the pines of the Pacific Islands, the 

 spice-trees of the Eastern Archipelago, and the cin- 

 chonas of Southern America. The plants of the valley 

 of the Caucasus, and those which flourish amongst 



