THE COMPOSITION OF PLANTS AND ANIMALS 149 



Ash. — On burning a plant or animal substance the non- 

 volatile products as described above will be left in the form of a 

 gray or white ash. This ash represents the nonvolatile products 

 of the combustion and contains all of the inorganic constituents 

 and some part at least of the carbon, nitrogen, sulphur and phos- 

 phorus of the organic constituents together with any metallic 

 elements which may have been present in organic combination. 

 Therefore, this simple separation of a plant or animal substance 

 into volatile and nonvolatile products does not correspond 

 exactly to the organic and inorganic constituents present. It 

 does, however, indicate approximately their relative amounts. 



On making such a separation of the volatile and nonvolatile 

 products of combustion and determining the amounts present, 

 it is found that the organic constituents yielding volatile products 

 are much in excess of the inorganic constituents which yield 

 the nonvolatile products, or ash. The number of different 

 elements present in the latter are more than those in the former. 



The table on pages 1 50-1 51 gives some results of the deter- 

 mination of volatile and nonvolatile or ash constituents in some 

 common plant materials. 



We have thus shown that plants and animals consist of both 

 organic and inorganic constituents. The two classes of ma- 

 terials are, therefore, both essential to the life of the organism. 

 In animals, the skeleton portion of vertebrate animals is largely 

 inorganic, being chiefly calcium phosphate, Ca3(P04)2. The 

 other inorganic constituents are found mostly in the liquids or 

 secretions of the animal body such as blood, milk, urine and the 

 digestive fluids. All of these inorganic substances play an 

 important role in the life of the animal. Their action is, how- 

 ever, not well understood in most cases and is at least distinctly 

 different from the action of the organic constituents. We shall, 

 therefore, not consider them in detail, simply stating that in the 

 animal body they are formed from the inorganic materials in 

 the food which the animal eats. 



In plants the inorganic constituents are related directly to 

 the soil, from which source the plant obtains its food material 



