FIRST REPLY. 145 



consumes a certain quantity of substances devoid of nitro- 

 gen, which are afforded him both by the fat of animals, 

 and, in the greatest abundance, by the majority and most 

 widely distributed of the vegetable substances. 



We now readily comprehend some of the most 

 striking phenomena of the mode of respiration of man 

 and animals. Nations of hunters and carnivorous ani- 

 mals, require a large quantity of their usually fatty 

 nourishment. In violent corporeal activity, they first 

 decompose their nitrogenous food into two constituents, 

 one containing the whole of the nitrogen, another which 

 contains a part of the carbon and hydrogen, and the latter 

 is applied to the purposes of respiration, since on account 

 of the incombustibility of nitrogen, the nitrogenous sub- 

 stances are not fitted for it. Hence comes the explanation 

 of the inquiet, restlessly active habits of the rapacious 

 animals, as of the hunter, since only by violent efforts of 

 the body can they decompose so much nitrogenous food, 

 and furnish the necessary material for the respiratory pro- 

 cess. The great quantity of nutriment which such a mode 

 of life requires, is likewise explained by this, particularly as 

 much more animal life is usually destroyed than imme- 

 diately corresponds to the requirements of nutrition. From 

 both causes the carnivorous animals, as well as the 

 nations of hunters, require an extended area for their 

 existence, and this condition always necessitates scanty 

 population. 



Where the breeding of cattle is carried on, we have a 

 transitional state, since Man here makes use of the domestic 

 animals to provide himself, in addition to meat, with the 

 substances devoid of nitrogen, in the constituents of milk 

 and the rich fat of the domestic animals, which is almost 

 wholly absent in the wild kinds. 



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