THE COMPONENTS OF PLANTS AND ANIMALS 5 



non-nitrogenous and nitrogenous substances. Under the former 

 are included the carbohydrates, the fats, the organic acids and 

 various other minor groups. The nitrogenous substances in- 

 clude the proteins and a variety of simpler nitrogenous sub- 

 stances sometimes classed together as the non-proteins. In the 

 following sections these various groups will be considered as 

 far as is requisite for an intelligent study of their behavior in 

 the animal body, it being assumed that the reader has already 

 some knowledge of their general properties, both chemical and 

 physical. 



5. Mineral matter, or ash. To what extent the elements 

 found in the ash and commonly reckoned as the mineral ele- 

 ments, namely, potassium, sodium, calcium, magnesium, iron, 

 phosphorus, sulphur, chlorin, silicon, etc., are actually present 

 in the living plant or animal as electrolytes and to what extent 

 as ingredients of complex organic molecules, it is at present im- 

 possible to state with any defmiteness. In ordinary usage the 

 term ash is equivalent to the residue remaining after incineration 

 at as low a temperature as possible, usually not exceeding a 

 dull red heat. 



The proportion of ash in ordinary feeding stuffs varies con- 

 siderably according to the kind of plant, the portion of the plant 

 used (seeds, stems, leaves, roots, etc.), the maturity of the 

 plant and various other conditions. Wolff gives the following as 

 general averages for the proportion of ash in the dry matter : 



The proportion varies most in the straw and least in the grain. 

 In the animal, the presence of ash is most evident in the bones. 

 About two-thirds of the dry matter of the clean bone (free from 

 fat) consists of ash. Ash is by no means absent from the soft 

 tissues of the body, however, of which it forms an essential in- 

 gredient. The proportion varies in different organs, but as 

 a rough general average the body, inclusive of the skeleton, 

 con tarns about 3.5 per cent of ash in the fresh substance, 



