COMPOSITION OF ANIMAL8 183 



organic matter or volatile matter, and tin- part remain* 

 in<; as ash is called inorganic matter, mineral matter, or 

 ash. 



173. Organic Matter. — The organic, or volatile 

 matter, of animal bodies may be divided into two 



compounds, one class containing nitrogen, 

 and the other containing no nitrogen. . Just as in the 

 case of plants, the nitrogen-containing compounds arc 

 called protein, and the compounds containing no nitro- 

 gen arc called non-nitrogenous substances. These com- 

 pounds are, however, quite different in appearance from 

 those found in plants, though they arc made Up of the 

 same elements. The relative proportions of these two 

 classes of substances arc quite different in animal 

 bodies from what they arc in plants. In nearly all 

 plants then are more of non-nitrogenous compounds 

 than of nitrogenous, but in animals the reverse Is true. 

 The animal body contain- Si a rule more nitrogenous 



substances than non-nitrogenous. 



174. Nitrogenous Substances: Protein. — The dry 

 matter of the muscles, nerres, and tendons of animal 



bodies is made up almost entirely of DJttOgen com- 

 pounds. The hoofs, horns, claws, skin, blood, hair, 



and bones contain considerable amounts of nit i 



The greater part of the bodies of animals is made np 



of compounds <»f nitrogen, though of course the differ- 

 ent parts of the body contain different amounts The 

 bones and skin, for instance, contain less nitrogen than 



the flesh. These nitrogen compounds of animal bodies 

 are made up of exactly the same elements that make 

 up those of plants; namely, earbon, oxygen, hydr 



