292 CHEMISTRY. 



that organic bodies are composed of the same elements as 

 mineral bodies, and while this is perfectly true, the state- 

 ment must be qualified. The number of elements which 

 enter into the composition of organic bodies is compara- 

 tively small. You remember there are sixty-three element- 

 ary substances at present known to the chemist : now of 

 these four build up nearly the whole of the innumerable 

 organic bodies ; these four are carbon, hydrogen, oxygen, 

 and nitrogen. 



Some of the other elements occur, it is true, but to a 

 comparatively limited extent. Thus we have calcium and 

 phosphorus in the bones, iron in the blood, silicon in tho 

 stalks of grains and grasses, and various other elements 

 in very small quantities for various purposes. The four 

 grand elements C, H, O, and N we have learned about in 

 studying mineral chemistry; one of them, you observe, is 

 a solid, while the other three are gases. They are all with- 

 out taste or smell, and the solid element is in its ordinary 

 form of a dark color ; and yet from these few materials 

 what an endless variety in taste, smell, color, and other 

 properties is produced in the vegetable and animal world ! 



Let us not be understood to say that other elements be- 

 sides the four C, II, O, and N are of little importance. 

 They are not only of use in their place, but they are essen- 

 tial, some of them as much so within a certain range as the 

 grand elements. 



408. Sources of the Elements in Organized Substances. 

 The elements of which vegetable and animal substances 

 are composed come from three sources earth, air, and 

 water. In the case of the plant they enter by the root and 

 the leaves. By the root, with its millions of little mouths, 

 they are drunk up dissolved in water, and in the sap 

 they flow upward to the leaves, where carbon is added 

 from the air. It is in the leaves that the sap, the build- 



