42 THE PLANT. 



recollect that the nitrogenous substances are neces- 

 sary to the formation of muscle in animals, for if 

 plants were allowed to complete their growth with- 

 out a supply of nitrogen, our grain and hay might 

 not be sufficiently well supplied with it to keep our 

 oxen and horses in working condition, while under 

 the existing law, plants must be of nearly a uniform 

 quality, (in this respect,) and if a field is short of 

 nitrogen, its crop will not be large, and of a very 

 poor quality, but the soil will produce good plants 

 as long as the nitrogen lasts, and then the growth 

 must cease.*" 



ANIMALS. 



That this principle may be clearly understood, it 

 may be well to explain more fully the application of 

 the different constituents of plants in feeding animals. 



Animals are composed (like plants) of atmospheric 

 and earthy matter, and every thing necessary to build 

 them up exists in plants. It is one of the offices of 

 the vegetable world to prepare the gases in the 

 atmosphere and the minerals in the earth for the 

 uses of animal life, and, to effect this, plants put 

 these> gases and minerals together in the form of the 

 various compound substances which we have just 

 described. 



In animals the compounds containing no nitrogen 

 comprise the fatty substances, parts of the blood, 

 etc., while the protein compounds, or those which 



* It is of course assumed that the soil is fertile in other re- 

 spects. 



