COMPOSITION OF ANIMAL MANURES. 175 



garded, in some respect or other, as manure. 

 During their life, the inorganic components of 

 plants which are not required by the animal system, 

 are disengaged from the organism, in the form of 

 excrements. After their death, their nitrogen and 

 carbon pass into the atmosphere as ammonia and 

 carbonic acid, the products of their putrefaction* 

 and at last nothing remains except the phosphate 

 of lime and other salts in their bones. Now this 

 earthy residue of the putrefaction of animals must 

 be considered, in a rational system of agriculture, 

 as a powerful manure for plants, because that which 

 has been abstracted from a soil for a series of years 

 must be restored to it, if the land is to be kept in 

 a permanent condition of fertility. 



We may now inquire whether the excrements of 

 animals, which are employed as manure, are all of 

 a like nature and power, and whether they, in every 

 case, administer to the necessities of a plant by an 

 identical mode of action. These points may easily 

 be determined by ascertaining the composition of 

 the animal excrements, because we shall thus learn 

 what substances a soil really receives by their 

 means. According to the common view, the action 

 of solid animal excrements depends on the decaying 

 organic matters which replace the humus, and on 

 the presence of certain compounds of nitrogen, 

 which are supposed to be assimilated by plants, and 

 employed in the production of gluten and other 

 azotised substances. But this view requires further 



