CHAPTER XXXVII 

 ANIMAL LIFE AND ANIMAL PRODUCTS. FOODS 



ONLY a few of the more important points in the chemistry 

 of animal life and growth can be touched upon here. In the same 

 way, the chemistry of foods is presented merely in outline. Some 

 food products, derived from plants, have been described in earlier 

 chapters. The single animal product dealt with in any detail in 

 the present chapter is soap. In connection with soap, the subject 

 of colloids is also briefly discussed. 



Composition of the Human Body. The following gives, 

 roughly, the percentage of each element in the human body. 



We have already learned that the calcium and phosphorus are 

 chiefly in the bones (p. 412). The nitrogen, sulphur, and iron are 

 in the proteins. The sodium is largely present as salts, in the 

 fluids of the body. The potassium is in the soft tissues and in 

 special secretions like milk. As in the plant, the carbon, hydrogen, 

 and oxygen are in the form of carbohydrates, proteins, and fats, 

 and there is also much water. 



Certain amounts of all these elements leave the system daily. 

 Water evaporates from the lungs and skin. The carbon leaves 

 in large amounts, chiefly from the lungs as carbon dioxide, and 

 also as excreted fats, proteins and carbohydrates. Much of the 

 nitrogen is eliminated, chiefly as urea CO(NH 2 ) 2 . The salts 

 are removed in the same way. 



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