PRACTICAL AGRICULTURE. 35 



inquiry is, what class of substances contain and yield to 

 grain-plaiits most nitrogen ? Nature, by the ordinary 

 action of the atmosphere, furnishes as much nitrogen 

 to a piant as is necessary to its bare existence. But 

 plants do not exist for themselves alone : the greater 

 number of animals depend upon the vegetable world 

 for food ; and, by a wise adjustment of nature, plants 

 have the remarkable power of converting, to a certain 

 degree, all the nitrogen offered to them into nutriment 

 for animals. We may furnish a plant with carbonic 

 acid, and all the materials which it may require for its 

 mere life ; we may supply it with vegetable matter in a 

 state of decay in the most abundant quantity ; but it 

 will not attain complete development unless nitroo-en 

 be afforded to it by the supply of suitable manure :°an 

 herb will indeed be formed, but its seeds or grain will 

 be imperfect and feeble. 



But when, with proper manure, we supply nitrogen 

 in addition to what the plant would derive from natural 

 sources, we enable it to attract from the air the carboa 

 which is necessary for its nutrition ; that is, when that 

 in the soil is not sufficient, we afford it a means of fixing 

 the atmospheric carbon. 



There are two principal descriptions of manure, the 

 beneficial agency of which is deriveable almost exclu- 

 sively from the large quantity of nitrogen they yield. 



These are the solid as well as fluid excrements of man 

 and animals. 



Urine is employed as manure, either singly, in its 

 liquid state, or with the faeces which are impregnated 

 with it. It is the urine contained in night-soil which 

 gives it the property of giving off ammonia, a property 

 which the discharges from the bowels possess only in a 

 very slight degree. Liquid manures act chiefly through 

 the saline substances they hold in solution ; while the 

 solid manures, even of animal origin, contain insoluble 

 matters which decay slowly in the soil, and there become 

 useful only after a time. When we examine what sub- 

 otances we add to a soil by supplying it with urine, we 

 find that this liquid contains in solution ammoniacal 



