ANIMAL CHEMISTRY. 395 



combination chiefly with sodium, forming the chloride or 

 common salt, which, as you will soon see, plays quite a 

 part in the animal economy. So phosphorus is mostly 

 united with oxygen and calcium, so as to form a phosphate 

 of calcium, and is never found as phosphorus. The com- 

 binations of the four grand elements are very various in 

 their character, for out of them are built animal structures 

 of every kind. It is not commonly the elements them- 

 selves, but the combinations of the elements, derived from 

 various sources vegetable, animal, and mineral that an- 

 imal chemistry works upon as materials in evolving ani- 

 mal substances, both liquid and solid. Thus phosphorus 

 and oxygen and calcium are not introduced into the an- 

 imal system separately, and there united to form phos- 

 phate of calcium; but this salt is introduced as such in 

 both vegetable and animal food. So the carbon, oxygen, 

 hydrogen, nitrogen, and sulphur which compose albumen 

 do not unite in the animal to produce this substance, but 

 it is formed in the vegetable for use in the animal. 



558. How Animal and Vegetable Chemistry are Alike. 

 They are alike, as you have just seen, in the elements which 

 are employed. They are also alike in many of the com- 

 binations of these elements. The chloride of sodium and 

 the phosphate of lime found in animals are also present in 

 vegetables. One of the principal constituents in animals 

 is like vegetable gluten. Then there are albumen and 

 casein, corresponding with substances of the same name in 

 vegetables. This resemblance between animal and vege- 

 table chemistry comes in consequence of the fact that the 

 vegetable world is so largely engaged in preparing for the 

 animal world what it gathers up from the mineral world. 

 It not only transfers, but prepares, and many of its prepa- 

 rations are combinations which enter with little or no al- 

 teration into the composition of animal substances. 



