158 I5I^- SCHLlilDliN'S THEOKY OF AGKICULTURE. 



yard manure, and that the organic matters can be merely acces- 

 sories, and not the most important principles. 



It must be remembered, too, tiiat the animal world depends 

 ultimately for its existence on the vegetable kingdom, and there- 

 fore what animals reqiure for nourishment must be necessary and 

 not accidental constituents of plants. Manmialia want, for in- 

 stance, lime and phosphates for their bones, iron for the colouring- 

 matter of their blood, nitre for their bile, muriates for their 

 gastric juice, and probably they could not live without potash 

 and sulphur, which we find in all their fluids. These then of 

 necessity must enter into their composition, and in grasses flint is 

 indispensable, though we do not find that it exercises any important 

 function in animals. This latter principle is universally diffused, 

 while phosphates are comparatively rare, and therefore demand 

 the first consideration. They exist in animal manure, especially 

 in human ordure, combined with lime, magnesia, and ammonia 

 ill a soluble or insoluble form, and are supplied largely by bones, 

 which in England are imported extensively from the Continent. 



Tiiere are many tables which seem to indicate that manures 

 are profitable in proportion as they are rich in nitrogen ; but the 

 experiments from which they were derived were made under pre- 

 judiced view^s, and they show that their beneficial character is at 

 least as clearly indicated by their alkalies and phosphates, as 

 appears by the tables of HermbstJidt and Kuhlraann. Alkalies 

 are very generally diffiised in nature, though there are lands 

 almost destitute of them which require a proper admixture. 

 These besides generally form highly soluble combinations which 

 are easily carried away by water, and the plants which grow in 

 the neighbourhood of dung-hills and firm-yards are especially 

 those whose ashes abovuid in them. A great waste, therefore, 

 must occur, which ought to be carefully replaced. Chili salt- 

 petre, a natural nitrate of soda, has been mvich recommended. 

 That tlie alkali, and not the nitrogen, is the active principle here 

 appears from the fact that the increase in hay and straw from 

 manure with nitrate of soda contains twice as much nitrogen as 

 the salt used for manure. Lime is a very general principle, and 

 as the carbonate and sulphate are not very soluble a good deal 

 remains in dung ; still there is waste, and some kinds of land are 

 naturally deficient in this principle. Marl and gypsum are the 

 great sources from which it can be artificially supplied ; the 

 latter also affords sulphur. Iron, magnesia, sulphuric acid, and 

 nuiriatic acid may be classed together, because they are of less 

 importance than the others, and need no particular observations. 

 Magnesia, though pi-esent in small quantities, seems to have an 

 important office (perhaps from its relation to phosphoric acid) ; 

 at least, it is surprising that in the ashes of most plants it bears a 

 greater projiortion to lime than it does in the soil. 



